Preheat your oven to 400°F (200°C). Line a large rimmed baking sheet — at least 18 by 13 inches — with aluminum foil and spray lightly with cooking spray, or use a 9-by-13-inch baking dish for a more casserole-style result. The sheet pan produces crispier potatoes and sausage; the casserole dish produces a more cohesive, slightly softer result. Both are delicious. Do not overcrowd — if you are doubling the recipe, use two pans.
Step 2: Season the Potatoes
In a large bowl, combine the potato pieces with 2 tablespoons of the olive oil and half of the seasoning blend — garlic powder, smoked paprika, onion powder, thyme, salt, and pepper. Toss until every piece is evenly coated. Spread the seasoned potatoes in a single layer on the prepared pan, ensuring no pieces are stacked on top of each other. Place in the preheated oven and roast for 20 minutes. This head start gives the potatoes time to begin softening and developing a golden crust before the sausage joins them.
Step 3: Add the Sausage and Vegetables
While the potatoes are in their first roast, toss the sliced sausage, onion chunks, and bell pepper pieces in the same bowl with the remaining tablespoon of olive oil and the remaining seasoning. After the potatoes have had their 20 minutes, remove the pan from the oven and add the sausage and vegetable mixture directly to the pan. Stir everything together gently so the sausage and vegetables settle in among the potatoes. Spread back into a single even layer as much as possible. Return the pan to the oven and continue roasting for 20 to 25 more minutes, stirring once halfway through, until the potatoes are completely fork-tender and golden at the edges, and the sausage rounds are caramelized and beginning to brown on both sides.
