Toast the 2 pieces of whole wheat toast until the bread is just golden brown.
Sprinkle the cheese evenly over the bread and melt in the microwave or oven until the cheese is just melted.
Cut the avocado in half lengthwise. Remove the pit from the avocado and discard. Remove the avocado from the skin and place the avocado flesh into a medium bowl and mash it with a fork and a squeeze of the fresh lemon juice. Add the chopped tomato and stir to combine. Season with salt and pepper as needed.
Divide the mashed avocado on top of the 2 pieces of cheesy toast.
Sprinkle with salt and pepper and serve immediately.