You don't need a grill to make these sweet and tangy Roasted Bratwurst with Peppers and Onions because the oven does all the work.
Preheat the oven to 400ºF. In a small bowl stir together the olive oil, red wine vinegar, coarse mustard, garlic powder, salt, and pepper. Set the vinaigrette aside.
Slice the bell peppers and onion into 1/4-inch strips and place them on a large baking sheet. Add the bratwurst links to the baking sheet, then drizzle the vinaigrette over top. Toss the peppers, onions, and bratwurst until everything is coated in vinaigrette.
Place the baking sheet in the oven and roast for 20 minutes, then give everything a good stir. Return the baking sheet to the oven and roast for another 20-25 minutes, or until the bratwurst, peppers, and onions, have browned on the edges.
Stuff the bratwurst, peppers, and onions into the buns and top with shredded cheddar if desired. Place them back in the oven for about 5 minutes to melt the cheese and toast the buns. Top with more mustard just before serving.