Preheat oven to 325F. Season bacon with black pepper and coat with brown sugar on both sides.
Arrange bacon in a single layer on a parchment paper lined with aluminum foil and bake until bacon is golden brown and crispy, about 20 minutes. Bacon will crisp up more when cooled.
Meanwhile, spread Dijon mustard on toast and layer with cheese, turkey, tomato, and lettuce.
Top with another toast, then bacon and avocado, and top with another slice of toast, mustard side down.
Cut into triangles and secure with toothpicks before serving.