Preheat the oven to 200°C (180°C fan). Line a large roasting tin with baking parchment.
In a large bowl, combine the kielbasa slices, potato pieces, pepper strips and onion wedges.
Drizzle with olive oil, sprinkle over the smoked paprika, garlic powder, dried oregano, salt and black pepper, then toss to coat evenly.
Spread the mixture out in a single layer in the roasting tin so that the pieces aren’t overcrowded.
Roast for 25–30 minutes, stirring halfway through, until the potatoes are tender and golden and the kielbasa is heated through and starting to caramelise.
Remove from the oven and, if you like, sprinkle over the chopped parsley before serving.