Heat oven to 450°F. Line baking sheet with foil. Cut peppers in half, and remove stems and seeds. Place cleaned peppers cut side down on baking sheet, and roast until charred, about 20 minutes. Carefully fold foil up around peppers and crimp edges to seal. let peppers sit in foil until cool enough to handle; them remove, peel, and chop.
Place chopped peppers, yogurt, Tabasco sauce, salt, pepper, and minced garlic in blender, and pulse to puree. Transfer to bowl, and stir in mayonnaise.