Heat 1 tablespoon oil in a large skillet over medium heat. Add frozen pierogies and cook, turning occasionally, until golden brown, about 8 minutes per side. Keep warm until ready to serve.

At the same time, cook bacon in a large, deep skillet over medium-high heat until evenly browned, 7 to 10 minutes. Remove bacon to a paper towel-lined plate, reserving drippings in the pan.

Add cabbage and onion to the bacon drippings. Stir, cover, and cook over medium heat for 10 minutes. Stir in tomatoes, remaining 1 tablespoon oil, vinegar, sugar, and salt. Add bacon and cook, uncovered, for 5 minutes.

Combine pierogies with the cabbage mixture and serve.