Preheat the oven to 400°F. Lightly grease the cups of a 12-cup muffin pan.
In a large bowl, add cooked rice, chicken, vegetables, onions, half of the cheese, and eggs. Mix well.
Spoon mixture into each muffin cup to ¾ full. Top each with remaining half of cheese.
Bake for about 15 minutes until the tops begin to turn golden brown and cheese is melted. Remove from oven and let sit in the pan for a few minutes. Loosen the edges with a knife and remove; place on a plate to cool slightly.