Heat the oil in a large sauce pan over medium heat. Add onions and garlic and sauté for 2 -3 minutes until soft and translucent.
Add tomatoes and season with salt and freshly ground pepper.
Bring tomatoes to a boil, turn heat down to low and simmer for 8-10 minutes, stirring occasionally until tomatoes have reduced and slightly thickened.
Stir in zucchini and simmer for an additional 10 minutes, until zucchini have softened.
Bring a large pot of water to a boil. Add pierogi and cook stirring occasionally for 5 minutes.
Drain pierogi and toss in with sauce and zucchini.
Add to platter and Garnish with parsley.