Step 1: Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper for easier cleanup.
Step 2: In a large mixing bowl, combine the diced potatoes, chopped onion, and sliced bell pepper. Drizzle with 2 tablespoons of olive oil, then sprinkle with dried rosemary, garlic powder, paprika, salt, and black pepper. Toss everything together until the vegetables are evenly coated.
Step 3: Slice your Italian sausage into 1-inch thick rounds. Add the sliced sausage to the bowl with the seasoned vegetables. Drizzle with the remaining 1 tablespoon of olive oil and toss gently to combine everything well.
Step 4: Spread the sausage and potato mixture in a single layer on the prepared baking sheet. Ensure not to overcrowd the pan; use a second baking sheet if necessary to allow for proper roasting and browning.
Step 5: Roast for 20 minutes, then remove the pan from the oven and carefully flip the sausage and vegetables with a spatula. Return to the oven and continue roasting for another 10-15 minutes, or until the potatoes are fork-tender and golden brown, and the sausage is cooked through and lightly caramelized.
Step 6: Once cooked, remove from the oven and let it rest for a few minutes before serving. Garnish with fresh parsley or chives, if desired.