Combine the yogurt, scallions, lime juice and 3 tablespoons water in a small bowl; season with salt. Refrigerate until ready to serve.
Combine 2 tablespoons butter with the paprika in a large microwave-safe bowl; microwave until the butter melts, about 30 seconds.
Add the frozen pierogi and toss to coat.
Spread the pierogi on a foil-lined baking sheet, transfer to the oven and bake, flipping halfway through, until golden, 20 to 25 minutes.
Meanwhile, melt the remaining 2 tablespoons butter in a wide pot over medium-high heat.
Add the onion and cook, stirring, until golden brown, about 8 minutes.
Add the cabbage, curry powder, 3/4 teaspoon salt and a splash of water and cook, stirring occasionally, until the cabbage is tender, about 12 minutes. (
Add another splash of water, if necessary.) Season with salt.
Divide the cabbage and pierogi among plates; serve with the yogurt sauce.