In a mixing bowl, add the mayonnaise, 1 tablespoon of the lemon juice, the lemon zest, garlic, salt, and pepper. Stir to combine, and then set aside.
For the crostini, preheat the oven to 350 degrees F.
Place the bacon slices on a baking sheet, sprinkle freshly ground black pepper all over the bacon, and place into the oven until cooked and crispy, 15 to 20 minutes. Once done, remove from the oven and cut each slice into thirds, then set aside.
Place the bread slices onto a baking sheet, drizzle with a little olive oil, and bake in the oven until slightly golden, about 12 minutes.
Once done, remove from the oven and set aside. Peel and remove put from the avocado then thinly slice, and drizzle the remaining tablespoon of lemon juice over the avocado slices to prevent browning.
To assemble the crostini, smear the mayonnaise mixture, then add 2 to 3 thin slices of avocado, 3 to 4 thin tomato slices, bacon, and a cheese shaving. Enjoy!