In a large bowl, combine the cream of mushroom soup, sour cream, garlic powder, onion powder, paprika, salt, and pepper. Mix until well combined.
In the bottom of the crockpot, layer half of the frozen pierogi. Top with half of the sliced kielbasa and half of the diced onion. Pour half of the soup mixture over this layer.
Repeat the layers with the remaining pierogi, kielbasa, onion, and soup mixture.
Cover the crockpot and cook on low for 6 to 8 hours or on high for 3 to 4 hours, until the pierogi are tender and heated through.
About 30 minutes before serving, sprinkle the shredded cheddar cheese on top. Cover and allow the cheese to melt.
Once done, garnish with fresh parsley before serving.