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!
Notes
Do I need to add tomatoes? No, if you don't want to, don't add tomatoes. 50% of the time I add tomatoes, the other 50% of the time I don't add tomatoes (like the pictures for this post!). The tomatoes add a nice sweetness to the cabbage and onions that we really love, and if it's garden season there's definitely tomatoes going in, but they're not absolutely needed if you don't want.