Start by preheating your oven to 425 degrees Fahrenheit so it's fully hot by the time your veggies go in. While it heats up, peel and cube your sweet potatoes and slice your onion into thick pieces. Chop your garlic roughly instead of mincing it finely.
Add the sweet potatoes, onion, and garlic to your baking sheet, then drizzle with olive oil and sprinkle your seasoning over the top. Toss everything together right on the pan until it's evenly coated. Spread it all out in a single layer so nothing overlaps or steams.
Roast the vegetables for about 20 minutes, pulling the pan out halfway through to stir everything around. This step matters because it keeps the onions and garlic from scorching in one spot while everything else stays pale. Give it a good stir with your spatula and spread it back out evenly.
Once your veggies are starting to turn golden and tender, nestle the sliced sausage rounds in between the potato pieces, making sure the cut sides touch the hot pan. This helps them get that nice seared crust instead of staying pale and soft.
Slide the pan back into the oven for another 10 to 15 minutes, until the sausage is browned and the sweet potatoes are fork-tender all the way through. Pull everything out, give it a minute to cool slightly, and serve it straight off the pan.