Preheat oven to 400*. Coat a baking sheet with cooking spray.
Whisk egg, flour, scallions, horseradish, salt and pepper in a large bowl. Stir in vegetables, onions and bacon.
Shape into pancakes.
Heat 2 teaspoons oil in a large nonstick skillet over medium heat. Cook 4 pancakes per batch. Transfer to baking sheet. Repeat until all batter is used, adding 2 teaspoons oil to each additional batch. Place baking sheet in oven and bake for 15 minutes. Serve garnished with sour cream.