Preheat the oven to 425°F (220°C). Line a large sheet pan with parchment paper or foil for easy cleanup.
A heavy-duty, rimmed baking sheet works best to prevent warping.
Prep the potatoes. Halve baby potatoes or cut larger potatoes into 1-inch chunks. Pat them dry with a paper towel to help them crisp in the oven.
Slice the sausage and vegetables. Cut the sausage into 1/2-inch pieces. Slice the onion and bell peppers into thick strips so they don’t burn.
Toss with oil and seasonings. In a large bowl, combine potatoes, peppers, and onions.
Add olive oil, salt, pepper, smoked paprika, garlic powder, oregano, and red pepper flakes if using. Toss until everything is evenly coated.
Spread on the sheet pan. Arrange the vegetables in a single layer on the pan. Scatter the sausage pieces evenly over the top.
Avoid overcrowding to encourage browning.
Roast for 25 minutes. After 25 minutes, stir and flip the potatoes and sausage to promote even crisping.
Roast 10–15 minutes more. Continue cooking until the potatoes are tender and golden with crisp edges, and the sausage is browned at the edges. Total time is usually 35–40 minutes.
Finish and serve. Taste and adjust salt as needed. Add a squeeze of lemon, sprinkle with parsley, or dust with Parmesan for a bright finish.
Serve hot right from the pan.