01 - Preheat the oven to 425°F. Line a large baking sheet with parchment paper or foil for easy cleanup.
02 - In a large bowl, combine the sliced bell peppers, red onion, and minced garlic. Drizzle with olive oil, and sprinkle with oregano, basil, red pepper flakes, salt, and black pepper. Toss to coat evenly.
03 - Spread the vegetables evenly on the prepared baking sheet. Nestle the sausages among the vegetables.
04 - Roast in the preheated oven for 25-30 minutes, turning the sausages and stirring the vegetables halfway through, until the sausages are cooked through (internal temperature 160°F) and the vegetables are tender and slightly caramelized.
05 - Remove from the oven and let rest for a few minutes. Slice the sausages if desired and sprinkle with fresh parsley and Parmesan. Serve hot.