Preheat your oven to 400°F (200°C).
Prepare a large baking sheet by lining it with parchment paper.
In a large bowl, combine the frozen pierogies, sliced kielbasa, red onion, and bell pepper.
Drizzle olive oil over the mixture and season with garlic powder, smoked paprika, salt, and pepper.
Toss the mixture until well coated and spread evenly on the prepared baking sheet.
Roast in the oven for 25–30 minutes, tossing halfway through.
Remove from the oven and check for doneness; the pierogies should be golden with crispy edges.
Garnish with freshly chopped parsley before serving.