Preheat a nonstick skillet over medium heat. Place the bread in the skillet and toast for about 3 minutes on each side or until golden and slightly crisp.
In a small bowl, mash the avocado with the lemon juice, salt, and pepper until smooth. Spread the mashed avocado evenly over the toasted bread.
Top with the chopped bacon. If using, place some diced tomato and crumbled cheese on top as well. Serve immediately for a quick, healthy breakfast.