Preheat the oven to 425 degrees F and line a rimmed baking sheet with parchment paper. Place the onions on the prepared baking sheet and toss with 1 tablespoon olive oil and some salt and pepper. Spread the onions in an even layer and roast for 5 minutes. Remove the pan from the oven and push the onions over to one side.
Toss the orange and green bell peppers in a medium bowl with the remaining tablespoon olive oil and some salt and pepper. Place the seasoned peppers in the center of the baking sheet. Place the sausages in the empty area next to the peppers, spacing them evenly apart.
Roast until the onions are translucent and tender, the peppers are soft and charred in spots, and the sausage is completely cooked through, about 25 minutes. (For even cooking, turn the vegetables halfway through cooking.)
Cut the sausages into bite-size pieces and divide evenly between four hoagie rolls. Top with the peppers and onions.
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