Toast the bread slices in a toaster until golden and crisp.
In a mixing bowl, mash the avocado with a fork and mix in lemon juice, salt, and black pepper.
Heat a non-stick pan over medium heat and melt the butter.
Crack the eggs into the pan and cook until the whites are set but the yolks are still runny, about 3-4 minutes. For firmer yolks, cook a bit longer or flip the eggs to make them over-easy.
Spread the avocado mixture evenly over two slices of toasted bread.
Place a fried egg on top of each avocado-covered toast.
Top each sandwich with the remaining slices of toasted bread and gently press down.
Notes
For added flavor, sprinkle some chili flakes or add a slice of tomato or lettuce to your sandwich. Serve immediately for the best taste and texture.