Preheat oven to 375 deg F. Zest the lemon and mince the garlic. PAt spinach as dry as possible with a clean cloth.
Combine all ingredients, plus garlic and lemon zest, in the largest bowl you own. Gently combine until evenly mixed together.
Sprat two baking sheets with non-stick spray. Make meatballs. I use an ice cream scoop, and I’ll weigh mine to make sure each is ~2 oz (yes, I really do). Ball and put on the cookie sheets. You should get ~16-18 meatballs.
Spray tops of meatballs with cooking spray lightly. Bake for 10 minutes, then rotate pans in oven. Bake for another ~10 minutes or until 165 deg F in the center. Serve immediately with a squeeze of lemon.