In a small bowl, mash the avocado with the back of a fork until fairly smooth. Spread avocado on one slice of bread. Top with tomato, bacon, and then cheese. Top with a second slice of bread. Repeat with remaining ingredients to create 4 sandwiches.
Mist the griddle with olive oil cooking spray and transfer sandwiches to the hot griddle; cook 2-4 minutes per side or until slightly golden and cheese is melted. Serve warm.