Spray a medium pan with cooking spray and warm over medium low heat. Meanwhile, mash avocado in a small bowl, mixing with salt and pepper to taste. Spread avocado mash on one piece of pita (or whatever type of bread you are using). Place cheese on top of avocado, followed by tomato slices, and last 2 slices of cheese. Top with the remaining piece of pita and place in pan. Cover pan and allow bread to toast on one side, and cheese to melt slightly, (about 1-2 minutes). Flip sandwich carefully, and cover, toasting bread on the other side and melting the cheese the rest of the way.
Place sandwich onto a plate or cutting board and cut with a sharp knife or pizza cutter down the center, then again, diving the sandwich into four triangles. Enjoy with low sugar ketchup if desired! Enjoy!