1Season fish generously on both sides with salt and freshly ground black pepper; set aside.
2Heat oil in a large frying pan over medium heat. When it shimmers, add onion, jalapeños, garlic, chili powder, and cumin and season with salt and freshly ground black pepper. Cook until vegetables are soft and starting to brown, about 7 minutes. Add tomatoes, season with additional salt, and cook until tomatoes just begin to break down, about 2 minutes more.
3Create 4 spaces in the vegetables and nestle fish, skin side up, in the empty spaces. Cook until underside is golden in color, about 5 minutes. Flip fish over, add lime juice, and cook, scraping the bottom of the pan to incorporate any browned bits, until almost all the liquid is gone, about 2 minutes more.