I love eating these meatballs wrapped in pita bread with lettuce, red onion, tomato, chopped cucumber, and homemade tzatziki (plain nonfat Greek yogurt, shredded cucumber, garlic, dill, salt, and a squeeze of fresh lemon juice). They're also great served with tzatziki as an appetizer.
Heat oven to 450ºF. Coat bottom of a baking dish with oil.
Bring a small pot of water to a rapid simmer. Add the spinach and cook 1-2 minutes or until wilted. Drain and chop.
In a large bowl, combine ground chicken, bread crumbs, garlic, egg, chopped spinach, and feta; mix until just incorporated. Firmly roll the mixture into 12 balls, about 2 inches each; place in prepared dish. Bake 15-20 minutes, or until lightly browned and cooked through.