In a large bowl, combine the cream of mushroom soup, sour cream, garlic powder, onion powder, salt, and pepper. Mix until smooth.

In the bottom of the crockpot, layer half of the frozen pierogi, followed by half of the sliced kielbasa and half of the diced onion.

Pour half of the soup mixture over the first layer, then sprinkle with half of the shredded cheddar cheese.

Repeat the layers with the remaining pierogi, kielbasa, onion, soup mixture, and top with the remaining cheddar cheese.

Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the pierogi are tender and the cheese is melted.

Before serving, sprinkle with chopped parsley if desired.