Using a box grater, grate the onion into a large bowl.
Add turkey, broccoli cole slaw, oats, garlic powder, salt, egg substitute, and 1/4 cup ketchup. Stir until thoroughly mixed.
Line 9 cups of a 12-cup muffin pan with baking cups and/or spray with nonstick spray. Evenly distribute turkey-veggie mixture among the muffin cups, and top each with 1 teaspoon ketchup.
Bake in the oven until firm with lightly browned edges, 30 to 35 minutes.