1. Grill bell peppers, uncovered, over medium-high heat, turning often, 15 to 20 minutes or until charred on all sides. Place in a paper or plastic bag; seal and let stand 5 minutes to loosen skins. Peel peppers, remove and discard seeds; core and chop into large pieces, and place in a bowl. Set aside.
2. Grill onion, uncovered, over medium-high heat for 4 minutes on each side; remove to a platter, and cover loosely with aluminum foil to keep warm. Grill sausages, uncovered, turning occasionally, 20 to 25 minutes or until no longer pink inside. Place on a platter, and cover loosely with aluminum foil to keep warm.
3. Toss bell peppers with olive oil, vinegar, and basil; place on a large platter. Season with sea salt and pepper. Place onion and sausages on top. Serve warm with buns or lightly grilled flour tortillas, and garnish, if desired.