Preheat an outdoor grill to MEDIUM then coat with 1 tablespoon of olive oil. Or, heat the 1 tablespoon of olive oil in an indoor grill pan over medium heat until hot.
Add bell peppers and grill for 15 minutes or until soft and skins are charred; remove from heat and set aside.
In a medium skillet, heat 1 tablespoon of olive oil over medium heat. Add onion and saute for 10 minutes or until browned.
In a blender or food processor, place bell peppers, onion, garlic, herbes de Provence, salt and pepper along with remaining 2 tablespoons of olive oil; process until smooth, adding more olive oil if the mixture is too thick.
Transfer to a medium saucepan and cook over low heat until warmed through. Preheat oven broiler or outdoor grill to MEDIUM-HIGH. Broil/grill salmon steaks for 5 minutes per side. Serve with red bell pepper sauce.