Coat bread slices with cooking spray; place on a baking sheet. Bake at 400° for 5 minutes or until lightly toasted; set aside.
While bread bakes, heat oil in a large nonstick skillet over medium-high heat. Add garlic; sauté 1 minute or until lightly browned. Add spinach, pepper, and salt, and sauté 30 seconds or until spinach wilts. Place spinach mixture in a bowl. Chill 5 minutes to quickly cool. Stir in tomato and vinegar. Top each bread slice evenly with cheese and about 2 tablespoons spinach mixture. Serve immediately.