Preheat oven to 375 degrees. Spray the muffin tins with cooking spray.
Place meat into a large mixing bowl. Chop spinach, finely chop carrots, mushrooms, onions; add to meat along with remaining ingredients. Mix well with your hands.
Place an even amount into muffin tins. Bake for 25-30 minutes, until meat is no longer pink in the center. Meanwhile, cook rice according to package directions.