Bring a saucepan of water to a boil. Carefully add the sausages and cook for approximately 10 minutes. Remove them from the water, let them cool slightly, and cut them into 1-inch pieces.
While the sausages are cooking, prepare the vegetables. Cut the onion, bell peppers, and optional celery into evenly sized 1-inch pieces.
Heat the oil in a large skillet over medium heat. Add the onion, bell peppers, and celery. Cook for 5–7 minutes, stirring occasionally, until the vegetables are tender but still have a little texture.
Add the sliced sausage, parsley, garlic powder, onion powder, salt, and pepper. Stir well and cook for another 2–3 minutes, or until the sausage is hot and the seasonings are evenly distributed.
Serve warm on its own, over rice or pasta.