Preheat your grill or grill pan to medium-high heat, around 400–450°F.

Slice multi-colored bell peppers and red onion into strips and toss in a large bowl with olive oil, kosher salt, and ground black pepper.

Place the Italian sausages or bratwurst directly on the grill and cook for about 5–7 minutes per side until the internal temperature reaches 160°F.

Add seasoned bell peppers and onions to the grill and cook for about 5–7 minutes until tender and slightly charred.

Remove sausages and vegetables from the grill, allowing the sausages to rest for about 5 minutes on a cutting board.

Slice the sausages and serve alongside grilled peppers and onions or in toasted rolls.