01 - Preheat the oven to 425°F. Line a large rimmed baking sheet with parchment paper or aluminum foil for easy cleanup.
02 - In a large mixing bowl, combine the sliced bell peppers, red onion, and minced garlic. Drizzle with olive oil, then sprinkle with oregano, basil, red pepper flakes, salt, and black pepper. Toss thoroughly until all vegetables are evenly coated.
03 - Spread the seasoned vegetables evenly across the prepared baking sheet. Nestle the sausages among the vegetables, ensuring they are not overcrowded for proper roasting.
04 - Roast for 25 to 30 minutes, using tongs to turn the sausages and stir the vegetables halfway through cooking. Continue until sausages reach an internal temperature of 160°F and vegetables are tender with lightly caramelized edges.
05 - Remove from the oven and let rest for 3 to 5 minutes. Slice sausages into pieces if desired, then sprinkle with fresh parsley and Parmesan cheese. Serve immediately while hot.