Preheat the oven to 375 degrees . In a large bowl, beat the eggs with 1 teaspoon salt and 1/4 teaspoon pepper. In a large, ovenproof nonstick skillet, cook the bacon over medium-high heat until crisp, 5 to 7 minutes; drain on paper towels. Crumble the bacon. Reserve 3 tablespoons bacon fat in the pan and discard the rest.
Add the potatoes and carrots to the pan and cook over medium-high heat, stirring occasionally, until softened, about 5 minutes. Stir in the cabbage and onion, season with salt and pepper and cook until browned, about 5 minutes.
Stir the eggs into the vegetables. Cook until the edges begin to set but the center is runny, about 3 minutes. Transfer to the oven and bake until the eggs are set in the center and the edges are golden brown, about 10 minutes. Invert the frittata onto a large plate, then re invert onto a serving platter; cut into wedges. Serve with the sour cream, bacon and scallion.