Toast the slice of dark sourdough bread until crisp in a toaster or under the grill. Remove the flesh from the half avocado and place it in a bowl. Mash the avocado roughly with a fork and stir through the juice of a quarter lemon, a pinch of salt, and some pepper.
Bring a pan of water with a splash of vinegar to a boil and reduce the heat until the water simmers gently. Stir with a spoon to create a whirlpool in the water and carefully break the egg into it. Poach the egg for exactly three minutes, remove it with a slotted spoon, and let it drain briefly.
Place the warm sourdough toast on a plate. Spread the avocado mixture in an even layer over the bread. Place the drained poached egg carefully on top of the mashed avocado.
Sprinkle the egg and toast with the teaspoon of chili flakes. Finally drizzle the teaspoon of olive oil over everything and serve the dish immediately.