Toast the sourdough bread and set aside.
Meanwhile, remove the pit from the avocado and use a knife to cut the avocado flesh into cubes while still inside the skin. Use a spoon to scoop the diced avocado into a small bowl. Add the mayonnaise, garlic powder, salt, and Tapatio and mash with a fork until smooth.
Spread the avocado mixture on the toasted bread & set aside.
Add a splash of oil to a small nonstick skillet and warm over medium heat. Add the large egg and pan fry for about 1 minute. Flip with a spatula and cook for about 20 seconds longer, or until cooked to your liking (I like to keep my yolk runny). Use the spatula to transfer the fried egg to the avocado toast. Season with kosher salt and freshly ground black pepper to taste and serve. Enjoy with a grapefruit on the side if desired.