Cook bacon in a large skillet over medium heat until crisp, 5 to 10 minutes. Transfer to a paper towel-lined plate.
Meanwhile, mash avocado in a medium bowl. Stir in basil, mayonnaise, garlic, salt and pepper. Toast bread.
Spread about 2 tablespoons of the avocado mixture on 4 slices of toast. Top each with 4 pieces of bacon, 2 tomato slices, 1 lettuce leaf, 1/4 cup sprouts and the remaining toast.