Combine first 9 ingredients in a bowl. Shape turkey mixture into 12 meatballs.
Heat a large nonstick skillet over medium-high heat. Add 1 1/2 teaspoons oil; swirl to coat. Add meatballs to pan; cook 4 minutes, turning to brown on all sides. Add sauce and 1/2 cup water; cook 7 minutes. Place meatball mixture in a bowl.
Wipe out pan with paper towels; return to medium-high heat. Add remaining oil and garlic; cook 30 seconds. Add spinach; cook 2 minutes, stirring until wilted. Place bread pieces, cut side up, on a baking sheet; top evenly with spinach, meatball mixture, and cheese. Broil 1 minute or until cheese is melted.