For the Vegetables:

1. Slice the bell peppers and onion into strips.
2. In a separate pan, heat 1 teaspoon of olive oil over medium heat.
3. Add the sliced peppers and onion, and season with a dash of salt and pepper.
4. Cook, stirring occasionally, until the vegetables are soft (about 5-7 minutes). Remove from heat and set aside.

For the Steak:

1. In a bowl, mix lime juice, remaining olive oil, minced garlic, chili powder, cayenne pepper, salt, and pepper.
2. Place the Wagyu flank steak in a shallow dish or a resealable bag. Pour the marinade over the steak, ensuring it is well-coated.
3. Marinate the steak in the refrigerator for at least 1 hour (or up to overnight for more flavor).
4. Preheat a grill or skillet to medium-high heat.
5. Grill or sear the marinated steak for 4-5 minutes per side, or until it reaches desired doneness.
6. Remove the steak from the heat and let it rest for 5 minutes. Slice against the grain into thin strips.

Assembly:

1. Warm the tortillas in a skillet or on the grill.
2. Serve the steak with the cooked peppers and onions, topped with fresh cilantro and avocado slices.
3. Enjoy with your favorite toppings or salsas!