Preheat oven to 375 degrees F. On a box grater or in a food processor, grate cauliflower and transfer to a large bowl. Place cauliflower in paper towels or cheesecloth and wring out any excess water.
Add eggs, cheddar cheese, garlic powder and whisk until combined. Fold in cheddar cheese, ham, spinach and onion. Grease a muffin tin with cooking spray, then fill each one about two-thirds full. Bake for about 20-25 minutes, or until lightly golden.