In a large skillet, cook bacon until browned and crispy. Remove the bacon from the skillet and set aside, but keep the drippings in the skillet.
Add cabbage and onion to drippings in the skillet, cover with lid and cook on medium heat for 10 minutes, until vegetables are softened.
Remove the lid and add in tomatoes, vinegar, sugar, salt, pepper and bacon to the skillet, and cook for 5 more minutes, stirring often.
Cook pierogies according to the package and drain. Add pierogies into the skillet with cabbage ingredients, stir, and serve! Optional: I like to add chopped fresh chives on top to give it a little color on top! Hope you enjoy!