Place the avocado, Greek yogurt, and garlic in a medium bowl and combine thoroughly with a fork, leaving some small chunks of avocado in the mixture. Add the lime juice and cumin, and season with salt and black pepper, to taste. Stir to combine and cover tightly. Set aside.

Line a microwave-safe plate with paper towels and place the bacon strips on it. Cover the bacon with more paper towels and place in the microwave for 3-4 minutes on high, or until bacon is cooked through, but not too crispy. (Cook time will vary, so check after 2 minutes and adjust the remaining time as needed).

Brush one side of each piece of bread with the melted butter. Heat grill pan over medium heat and place bread, buttered side down, on the pan. Apply light pressure to each slice with a spatula, being careful not to move the bread in the process. Once nice grill marks have formed, remove from heat and set aside.

Allow bread to cool slightly, then add avocado spread to 2 of the slices on the non-grilled side. Divide the lettuce, tomato, and cooked bacon slices between the two sandwiches and top each with the remaining pieces of grilled bread. Cut in half and serve immediately with your favorite side dish or potato chips. Enjoy!