Toss the sausage, onion, bell peppers, and tomatoes in a bowl with 1 Tbsp. olive oil.
Season with salt and pepper.
Thread onto the skewers, alternating the sausage and vegetables. Place kebabs on grill and turn often, until the vegetables are slightly softened and the sausage begins to brown, about 5 - 6 minutes.
Brush skewers with the remaining olive oil and continue to grill, turning until the tomatoes are tender and sausage is slightly charred, about 4 - 5 minutes. Serve immediately. Be careful, skewers may be hot.