Preheat oven to 400°F (200°C). Remove stems and seeds from peppers, slice into quarters, toss with 1 tablespoon olive oil, salt, and pepper. Spread on baking sheet.
Roast peppers for 20 minutes until softened and slightly charred. Let cool for 5 minutes.
Transfer roasted peppers to blender with garlic cloves and lemon juice. Blend until smooth, about 30-45 seconds.
Heat remaining 1 tablespoon olive oil in large skillet over medium heat. Pat tilapia dry, season with salt and pepper.
Cook tilapia 3-4 minutes per side until golden brown and fish flakes easily with fork. Internal temperature should reach 145°F.
Pour roasted pepper sauce over cooked tilapia and simmer together for 1-2 minutes until heated through. Serve immediately.
Notes
Fresh tilapia works best, but frozen is fine if completely thawed and patted very dry. Cod or haddock can substitute.
Sauce can be made 2 days ahead and refrigerated. Reheat gently before serving.
For spicier version, add red pepper flakes to sauce or use one poblano pepper with one red bell pepper.