Heat the oven to 375° and coat a standard 12-cup muffin tin with cooking spray. In a large bowl, lightly beat the eggs. Stir in all but the last four ingredients, then gently mix in the ground beef.
Divide the mixture evenly among the muffin wells. Use your fingers to press down and pack the contents of each well. Cook the cupcakes for 20 minutes, then remove the pan from the oven and sprinkle a heaping tablespoon of cheese onto each cupcake. Return the pan to the oven and bake until a thermometer inserted into the center of a cupcake registers 160°, about 10 minutes more. Cool the cupcakes for 5 minutes before unmolding them. Serve with sour cream and scallions.