Preheat your grill to medium heat. Make sure the grill grates are clean.
Reduce one side to medium-low heat.
Place a cast iron pan with the olive oil and onions inside of it on the medium-low side of the grill. Cook for about 15 to 20 minutes, stirring from time to time, you want the onions to start to turn golden but not burn. Don't cook on high or you will just burn them. You want them soft, with crispy edges. About 5 minutes before the onions are perfect, add the roasted red peppers to the pan. Continue to cook and stir until they start to cook around the edges. Toss with salt and pepper.
Remove from grill very carefully (remember that pan is scorching hot so use mitts). Transfer to a plate lined with paper towels so you can drain off excess oil.
Place the Italian Sausage on the grill. Grill each side for about 2 to 3 minutes, until it's golden and has some beautiful char marks on the sides. Remove from grill and turn grill off
Place each sausage on each bun (you can toast them lightly if you like prior) and then pile the caramelized onion and roasted red pepper mixture over top.
Enjoy with a big old non-gassy smile.