Heat the broiler with a rack 6 inches from the heat source. Line a large, rimmed sheet pan with aluminum foil for easy cleanup, if desired (do not use parchment paper). Lightly spray the pan with nonstick cooking spray. Use a paring knife to score the sausages in a few places on both sides (be careful not to cut all of the way through). Place the sausages on the prepared sheet pan.

Add the peppers and onion to the pan. Drizzle olive oil over all the ingredients; toss to coat. Season with salt and pepper to taste; arrange everything in a single layer.

Place the pan under the broiler until the sausage is cooked through and the peppers and onions are nicely charred, about 10-15 minutes. Flip the sausages and stir the veggies halfway through. I like to keep a close eye on the pan while it’s under the broiler. If one or two of the sausages are getting darker than the others, just use a spatula or tongs to move them to a different spot on the pan. This allows all of the ingredients to cook evenly under the broiler. If the veggies and sausages are getting too dark before they’re cooked through, just tent loosely with foil.