Preheat broiler. In 12-inch nonstick skillet, heat oil on medium 1 minute. Add garlic and cook 3 to 4 minutes or until garlic is golden, stirring occasionally. Stir in spinach and cook 1 to 2 minutes or until spinach wilts. Stir in 1/8 teaspoon each salt and freshly ground black pepper. Remove skillet from heat.
Meanwhile, place bread on cookie sheet and toast in broiler 2 minutes or until beginning to brown.
Turn toasted bread over and spread Dijon on top of bread slices; top with spinach, sliced tomatoes, then cheese. Broil sandwiches 2 to 3 minutes or until cheese melts and begins to brown.