1. Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).
2. Place tomato halves onto a lined baking sheet, spray with cooking spray, and roast until beginning to shrivel, about 10 minutes. Remove from oven and set aside.
3. Place waffle squares on a lined baking sheet. Combine butter and garlic and brush waffle squares generously with the mixture. Layer each waffle as follows: a slice of avocado, two tomato halves, a slice of cheese, and some chopped basil. Bake at 400 degrees Fahrenheit (200 degrees Celsius) for 10 minutes.
4. While the waffles are baking, prepare balsamic reduction: Boil vinegar in a small pot for about 20 minutes, or until reduced and slightly syrupy. Add confectioners’ sugar and mix to combine. Remove reduction from heat and allow to cool. Remove waffles from oven and drizzle with balsamic reduction. Serve warm.