In a medium bowl, combine 2 Tbsp of oil, lemon juice, cumin, chili powder, and garlic. Mix well.
Stir in the cut-up fish and marinate for 20 minutes.
In a large skillet, heat the remaining 1 Tbsp of oil and sauté the onion and bell pepper over medium-high heat for 4-5 minutes or until tender but not brown.
In the last minute of sautéing, add the shredded cabbage. (set aside)
Add the fish mixture to the same skillet and cook for about 4 minutes; set aside.
Warm the soft tortillas gently on the stovetop or in a pan until slightly browned.
Place each tortilla on a plate and scoop a portion of the cooked fish and vegetables on top of it.
Top with Pico Di Gallo (or salsa) and avocado slices.
Sprinkle with chopped cilantro if desired.
Serve with lime slices