Begin by cooking the bacon in a skillet over medium heat until crispy, about 6-8 minutes. Remove the bacon from the skillet and let it drain on paper towels. Reserve a tablespoon of bacon grease in the skillet.
While the bacon is cooking, toast the slices of whole-grain bread until golden brown.
In the same skillet with the reserved bacon grease, crack the eggs and cook them to your desired doneness (sunny-side up, over-easy, or scrambled), seasoning with salt and black pepper. This should take about 2-4 minutes.
While the eggs are cooking, scoop the flesh of the avocados into a bowl and mash it with a fork. Season with salt and black pepper to taste.
Spread the mashed avocado evenly over each slice of toasted bread.
Top each avocado toast with a cooked egg and two slices of crispy bacon.
Sprinkle with red pepper flakes if desired and garnish with fresh cilantro or parsley. Serve immediately.