In a large bowl, combine the first seven ingredients. In another bowl, combine the eggs, squash, yogurt and oil; stir into dry ingredients just until moistened. Stir in corn and onions.
Coat muffin cups with cooking spray; fill three-fourths full. Bake at 425° for 12-16 minutes or until a toothpick comes out clean. Cool for 5 minutes before removing from pan to a wire rack. Serve warm.