Preheat oven to 425°F. Line a large rimmed sheet pan with parchment paper or foil for easier cleanup if you wish.
Add potatoes to a large bowl. Toss with 2 tablespoons olive oil, Italian seasoning, garlic powder, smoked paprika, salt, and pepper.
Arrange potatoes in a single layer on the baking sheet. Roast for 20 minutes.
In the same bowl, toss the sausage, green beans, onion, and minced garlic with the remaining 1 tablespoon of olive oil.
Remove the sheet pan from the oven. Add the sausage, green beans, onion, and minced garlic mixture. Spread into an even layer.
Return to the oven and roast for another 18 minutes, stirring once halfway through, until the potatoes are tender and the green beans are cooked to your liking. Serve immediately.
Notes
Use fresh green beans for the best texture. Frozen green beans may become too soft.
Spread everything out as much as possible on the pan so the sausage and potatoes brown instead of steam.
Smoked sausage, turkey kielbasa, or chicken sausage can be used in place of regular kielbasa.
In Canada, you may also see similar sausage sold as Polish sausage or kolbassa.
If cutting the potatoes ahead of time, keep them submerged in cold water in the refrigerator, then drain and dry them well before roasting.