Heat oven to 425°F. Brush 18-by-13-inch rimmed sheet with 1 tablespoon oil. Arrange frozen pierogies in one layer; drizzle measured water around them. Tightly foil-cover.
Bake 15 minutes; carefully uncover, avoiding steam. Turn pierogies; oven-evaporate pooled water 2 minutes.
Toss kielbasa, beans, and onion with remaining oil, salt, and pepper. Add around pierogies in one layer.
Roast uncovered 15 to 18 minutes, turning once, until pierogies tender with hot filling and golden surfaces and beans tender. Follow any higher package minimum internal temperature.
Mix sour cream and Dijon. Serve 3 pierogies per person with one-quarter sausage and vegetables and spoonful cold sauce.