Cook the bacon either in a skillet on top of the stove or in the oven on a pan lined with parchment paper at 375 degrees F. Turn after 6-8 minutes until its crispy but not burnt. Remove and place on a plate lined with paper towels. Set aside.
Lightly butter one side of each slice of bread and toast the buttered side of each slice in a skillet over medium-high heat. Remove when golden brown and plate for assembly.
With 2 slices per plate, toasted side down add mayo to either one or both slices. Add arugula to each side, next add a slice of tomato and avocado. Break bacon to fit the bread and add 3-4 slices per sandwich. Salt and pepper if desired and enjoy.