Heat grill. In small bowl, combine 2 tablespoons of the pesto, butter and roasted peppers; mix well. Refrigerate while preparing sea bass.
When ready to grill, sprinkle sea bass with pepper; brush with remaining 2 tablespoons pesto. Place fish, skin side down, on gas grill over medium-high heat or on charcoal grill 4 to 6 inches from medium-high coals. Cook 12 to 15 minutes or until fish flakes easily with fork. Serve sea bass with pesto butter.