Heat the oven to 400F.
Mix together the cumin, garlic powder, chili powder and salt in a small bowl.
Place the peppers and onions on a sheet pan. Drizzle with 2 tablespoons olive oil and 1 ½ teaspoons spice mix, tossing to combine.
Place in the oven and roast until lightly browned, about 10-15 minutes.
Meanwhile, in a medium bowl, toss the fish, 1 tablespoon olive oil, and remaining spice mixture.
Remove from the vegetables from the oven, and give them a flip and stir. Arrange the fish evenly between the vegetable, then place back in the oven.
Roast for an additional 10 minutes, or until the fish is cooked through and flakes easily with a fork. Sprinkle the lime juice over the pan.
Serve with whatever fajita fixins’ you like.