Prepare the marinade by mixing all of the marinade ingredients together in a bowl or shallow dish.
Slice up the steak into 1/2 by 1 inch strips. Place the steak in the bowl/dish with the marinade. Mix well so that all of the strips are covered with the marinade. Set aside to marinate while you prepare the rest of the ingredients.
Chop the onion, bell peppers and garlic as noted.
Lightly grease a large sheet pan with 1 tbsp avocado oil. Spread the onion and bell pepper out on the sheet pan. Drizzle with 1 tbsp avocado oil and lightly sprinkle garlic, salt and pepper over everything. Toss to coat.
Place in the oven to cook for 10 minutes.
Remove sheet pan from oven and turn the oven to broil.
Mix and push the vegetables to the sides of the pan. Add steak strips to the pan in a single layer, spreading them out as much as possible. Broil on high for 3-4 minutes or until steak is cooked to your liking. You may need to flip the steak pieces to cook on all sides.
Once the fajitas are cooked, remove from oven and allow to cool for a few minutes. Prepare toppings and shells/tortillas as desired.
To serve, spoon fajita mixture into shells/tortillas, top with avocado and cilantro and enjoy.
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