Cut the avocado in half, remove the pit, and scoop out the flesh with a spoon.
Mash the avocado with a fork, add salt, pepper, and lemon juice, and mix well.
Toast the whole wheat bread in a toaster.
Spread the mashed avocado evenly over the toasted bread.
Add vegetables of your choice such as tomato and lettuce.
Cover with the top slice of bread to complete the sandwich.