Cut peppers into quarters and take out the seeds. Roast peppers over open fire until they are black on the skin side only. Cut peppers julienne-style and put in a bowl. Add oil, lime juice and mesquite seasoning, then mix well and let marinate, refrigerated, for 12 to 24 hours.
Preheat oven to 400 degrees F.
Prepare a single fish fillet on a sheet of aluminum foil, skin-side down. Repeat with remaining fillets, preparing a sheet of foil for each.
Divide pepper mix on top of the fillets, then add onions. Transfer foil to baking sheets and bake, 7 to 8 minutes.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.