Line a large baking sheet with foil. Cut bell peppers in half, through the stem. Remove stem, seeds and ribs and face cut-side down on foil. Drizzle with 1 tablespoon olive oil and place in oven set to broil for 15 to 17 minutes, until skins are fully charred.
While peppers are roasting, add 1 tablespoon olive oil to a skillet over medium-high heat. Add onion and cook for 5 to 7 minutes, until translucent. Add in minced garlic and cook for 1 minute.
Remove peppers from the oven and set oven temperature to 400 degrees F. Carefully fold up the foil to create a sealed packet so the peppers steam inside. Let sit for 10 to 15 minutes, until peppers are cool enough to touch. Peel away and discard skins.
Add roasted peppers and cooked onion/garlic mixture to a blender with 2 tablespoons olive oil, balsamic vinegar, salt and pepper flakes. Puree until smooth.
Dry cod filets with a paper towel. Brush with olive oil and season liberally with salt and pepper. Place on a baking sheet, and bake on the middle rack for 12 to 14 minutes, until fish reaches 145 degrees in the thickest part and just begins to flake apart.
Pour red pepper sauce onto a rimmed plate. Arrange cod filets into the sauce, garnish with chopped basil and lemon wedges (optional) and serve.
Serving suggestion: Add a side of steamed, riced vegetables or roasted potatoes to soak up the Red Pepper Sauce.
Notes
Store leftover red pepper sauce refrigerated in a container with an air-tight lid.