Heat a medium pot of water to a boil. Add the pierogies and cook 3 min. Drain. Toss with 1 tbsp oil.
Meanwhile, heat remaining 1 tbsp oil in a 12-inch nonstick skillet on medium-high. Add the kielbasa and cook 2–3 min., until warm. Drain liquid from the onions and peppers. Add to skillet and cook 2–3 min., until slightly browned, stirring occasionally.
To skillet, stir in pierogies and cook 2–3 min., until pierogies are golden.