Wash and cut the potatoes into evenly sized bite-sized pieces. Slice the bell peppers and the onion, slice the sausage into rounds, and mince the garlic.
In a large bowl, combine the potatoes, bell peppers, onion and garlic. Drizzle with the olive oil and season with the Italian seasoning, smoked paprika, garlic powder, onion powder, salt, black pepper and the crushed red pepper flakes, if using. Toss everything together until evenly coated.
Heat a large skillet over medium-high heat. Add the sausage and cook for 4–5 minutes, until lightly browned. Remove and set aside, if desired.
Add the seasoned vegetables to the same skillet and cook for about 5 minutes, stirring occasionally, until they begin to caramelize.
Return the sausage to the skillet, cover, and cook over medium heat for 20–25 minutes, stirring every few minutes, until the potatoes are fork-tender.
For crispier potatoes, uncover the skillet for the last 5 minutes and increase the heat slightly.
Sprinkle with the fresh parsley and the Parmesan cheese just before serving.
Serve hot with crusty bread or a fresh green salad.