Heat olive oil in a large skillet over medium heat.
Sauté onion until translucent about 4 to 5 minutes, then add garlic and cook 1 minute more. Mix well.
Place fish on the skillet and cook until the flesh starts to flake.
Add jalapeño peppers, tomatoes, cilantro and lime juice. Sauté over medium-high heat for about 5 minutes, breaking up the fish with the spoon to get everything mixed well; season to taste with salt and pepper.
Meanwhile, heat tortillas on a skillet or directly over the flame of the burner a minute or 2 on each side to warm.
Serve a little over ¼ cup of fish on each warmed tortilla topped with cabbage, avocado, cilantro, and a squeeze of lime.
