Toast the sourdough slices until deeply golden and crisp.
Meanwhile, fill a medium pot with 3–4 inches of water and bring to a gentle simmer. If using, stir in the vinegar.
Crack each egg into its own small bowl. Swirl the simmering water with a spoon to create a gentle vortex, then slide in one egg (repeat with the second egg, or poach one at a time for the neatest shape).
Poach for 3–4 minutes, until the whites are set and the yolks are still soft. Lift eggs out with a slotted spoon and briefly drain on paper towels.
In a small bowl, mash the avocado with lemon juice, salt, and pepper until mostly smooth.
Spread 1 tablespoon cream cheese on each hot toast slice, then top with the mashed avocado.
Place one poached egg on each toast. Season with extra salt and pepper, and sprinkle with red pepper flakes and/or everything bagel seasoning if you like.
Serve right away with salad leaves, cherry tomatoes, and sprouts on the side (or piled on top).