Heat olive oil in a large frying pan over medium heat and sauté the onions until translucent about 4 to 5 minutes, then add garlic and cook 1 minute more. Mix well.
Place fish in the pan 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 in a dry frying pan or directly over the flame of the burner a minute or 2 on each side to warm.Divide the fish evenly between the tortillas, sprinkle over fresh coriander and a squeeze of lime