Preheat oven to 400°F.

Cut the kielbasa into 4-6 inch lengths and arrange around the outside of the sheet pan. Toss the onions and bell peppers with the olive oil, ½ teaspoon of kosher salt, and black pepper in a large mixing bowl then use your hands or tongs to move it to the pan, depositing it between the lengths of kielbasa.

In the same large mixing bowl you used for the peppers and onions, toss the pierogies with the remaining ingredients to coat, then arrange those in the center of the sheet pan. The goal is to get as many pierogies touching the surface of the pan as possible. Try not to have multiple layers of pierogies. Place the pan in the oven. After 15 minutes, try to remember to flip the pierogies over, having any that weren't touching the pan do so now. If you forget, it's not a disaster, but they'll be better if you remember.

Bake an additional 15 minutes, for a total of 30 minutes or until the pierogies are puffy and beginning to show signs of golden brown around the edges, the sausages are plump, and the onions are crisp tender. Serve immediately with a nice salad.