Costco Grilled Flap Steak Tacos with Avocado

Costco has packages of Beef Loin Flap Meat Steak for sale and they are one of the few places we have seen this cut of beef for sale.  These steaks are naturally on the thin side which makes them a great choice for grilling over high heat.

The Flap Steaks are Item Number 91385 and are found in the coolers at the butcher department of the Costco warehouse. The steaks, USDA Grade Choice, cost about $10 per pound and you get about two pounds per package for a cost of around $20.

This post is going to cover everything you need to know to make some delicious Grilled Flap Steak Tacos!

Package of Flap Steak from Costco

Prepare the Flap Steaks for Grilling

Our package of flap steaks weighed two pounds and contained three steaks.  We used two of the steaks for theses grilled tacos and saved the third for an incredible Beef and Broccoli Stir Fry.

There is very little fat on these steaks and trimming is not needed.

The three things you need to do to prep flap steak for the grill are:

  • Identify the Grain Pattern
  • Season the Steaks
  • Let the Steaks Warm Before Grilling

Grain Pattern of the Flap Steak

The flap is similar to a flank steak in that it has a highly defined grain pattern that travels the width of the steak.

You will want to take a minute before seasoning the steak to see the grain so you will understand how to slice it after it has been grilled.

It will be important to slice the flap AGAINST the grain after grilling for maximum tenderness.

Two Flap Steaks from Costco

Season the Steaks and Let Them Warm

Make up a dry rub for the steaks or use a commercial product like Traeger Beef Rub.  We wanted a Carne Asada flavor profile for our tacos so this is the rub we made:

  • 1 tbls Chili Powder
  • 2 tsp salt
  • 1 tsp black pepper
  • 1 tsp lemon zest

You could also use just about any commercial Taco Seasoning and it would be delicious.

Apply the rub to both sides of the steak and then let the steaks rest, covered, at room temperature for 45-60 minutes.  The resting period gives the rub some time to work its magic and will help the steak cook evenly.

Preheat Your Weber Gas Grill

We want to grill these at really high temperatures which is a perfect job for a Weber gas grill.  We were cooking on a Traveler but this would work equally as well on a Q2200 or any Weber full sized grill with a Sear Station.

This is not a job for a Traeger or a Pit Boss as they simply will get hot enough.

Turn your gas grill to High and let it preheat for at LEAST 15 minutes.  We want those cast iron grill grates to get as hot as possible.

Preheat your Weber Gas Grill

Grill the Seasoned Flap Steaks over High Heat

Put the flap steaks on the grill with plenty of space between them.

We realized we had plenty of extra space left so we threw on an avocado as well.  As long as we are grilling we might as well grill everything!

Close the lid and let the steaks grill for four minutes.

Open the lid, flip the steaks and grill for four to five more minutes until an internal temperature of 135-140F is reached. These are thin steaks that grill fast so hitting the exact internal temperature you want can be tricky.  Don’t worry if you overshoot by a few degrees.

Grill for four minutes per side

Slice and Serve the Grilled Flap Steak

Remove the grilled steaks and avocado halves from the grill.

Let the steaks rest for 10-15 minutes and use that time to finish the avocados.  To finish preparing the avocados, use a spoon to peel away the skin from the flesh of the avocado, slice thinly and sprinkle with fresh lime juice.

After the steak has rested slice the meat thinly across the grain.  It helps to have a proper slicing knife like a 14 inch granton edged slicer that has been recently sharpened.

Slices of Grilled Flap Steak

We prepared our tacos by serving with sliced avocado, grilled steak and salsa. You could add some pickled jalapenos, cream cheese or even pickled red onions if you wanted a different flavor profile.

We went with flour tortillas because they hold up better than corn tortillas…that being said, corn tortillas would have added a whole new layer of flavor.

Grilled Flap Steak and Avocado Taco

Grilled Flap Steak and Avocado Taco

Costco Grilled Flap Steak Tacos

Grilling the Flap Steak from Costco makes for easy and tasty tacos!
Prep Time 1 hour
Cook Time 10 minutes
Total Time 1 hour 10 minutes
Course Main Course
Cuisine American
Calories 317 kcal


  • Weber Gas Grill


  • 1.5 lbs Costco Beef Loin Flap Meat Steaks
  • 1 Avocado
  • Flour Tortillas
  • Salsa
  • Steak Rub Seasoning
  • 1 tbsp Chili Powder
  • 2 tsp Salt
  • 1 tsp Black Pepper
  • 1 tsp Lemon Zest


  • Season both sides of the flap steaks with the dry rub.
  • Let the season steaks rest, covered at room temperature for 45-60 minutes.
  • Slice an avocado in half and remove the pit.
  • Preheat your gas grill on High for 15 minutes.
  • Place the steaks and avocado halves on the grill and close the lid.
  • Grill the steaks for four minutes, flip and grill for another 4-5 minutes until an internal temperature of 135-140F is reached.
  • Take the steaks and avocado off the grill.
  • Scoop the avocado away from its skin, slice and give a squeeze of lime juice.
  • Slice the grilled steak thinly against the grain and assemble tacos as desired.
Keyword Costco Beef Loin Flap Meat Tacos