Remove flank steak from package and pat with paper towels. Score both sides of the meat across the grain slicing 1/8 inch deep, not all the way through.
Rub steak on both sides with 2 round tablespoons or two cupped palms of fajita seasoning. Place in a Ziploc bag. Pour in enough beer to cover the steak. Seal and marinate overnight.
Remove from refrigerator 30 minutes prior to grilling.
Slice onions in half moon rings ¼ inch thick. Slice peppers in half and remove the seeds. Slice bell peppers in ¼ in strips. Slice poblano pepper halves in 1/8 inch strips horizontally.
Combine onion and peppers in a large piece of heavy duty tin foil. Drizzle with olive oil, sprinkle with cumin, chili powder and ½ tsp salt. Mix together. Seal foil packet length wise and on the ends so nothing falls out.
Remove steak from beer marinade.
Place onion and pepper packet on grill, seam side down. Grill 5 minutes and turn over. Loosen top seal of foil to let some steam escape. Cook another five minutes while steak is grilling to medium rare about 130F.
Remove from grill and tent steak with foil. Let rest 10 – 15 minutes.
Cut steak across the grain in ½ inch thick slices. Serve with onion and pepper mixture and warm tortillas. Add toppings of sliced avocado or guacamole, cheese, sour cream, fresh tomatoes, and salsa.
Notes
Make your own Smoky Steak Fajita Seasoning
1 tbsp chili powder
1 ½ tsp kosher salt
2 tsp smoked paprika
1½ tsp ground cumin
1½ tsp garlic powder
1 tsp onion powder
1/4 tsp cayenne pepper (optional)
Mix all ingredients and store in an airtight container.