Preheat your grill or grill pan to medium-high heat, around 400°F. Allow about 10-15 minutes for the grill to reach the right temperature.

While the grill heats up, slice your multi-colored bell peppers and red onion into thin strips. Toss the vegetables with olive oil, kosher salt, and ground black pepper until well-coated.

Place the Italian sausages directly on the grates. Grill for about 5-7 minutes on each side, turning occasionally until golden-brown and cooked to an internal temperature of 160°F.

Add the bell peppers and onions to the grill after the sausages have cooked for about 10 minutes. Use a grill basket or wrap the vegetables in aluminum foil. Grill for 5-7 minutes until tender and slightly charred.

Remove the sausages and vegetables from the grill. Serve on a platter or stuff into toasted rolls for sandwiches.