Toast the sourdough bread until golden and crisp.
Cut the avocado in half, remove the pit, and scoop the flesh into a medium bowl.
Mash the avocado with a fork and season with salt and cracked black pepper.
Bring the water to a boil in a small saucepan, then reduce to a gentle simmer.
Add the white vinegar to the water.
Crack one egg into a small cup.
Stir the water gently to create a whirlpool and carefully slide the egg into the center.
Poach for 3–4 minutes until the egg white is set and the yolk remains soft.
Repeat with the second egg.
Spread the mashed avocado evenly over the toasted bread.
Slice the cherry tomatoes in half and arrange them on top of the avocado.
Carefully remove the poached eggs with a slotted spoon and place them on paper towels to drain briefly.
Place one egg on each slice of toast.
Finish the Avocado Toast with Egg and Tomato with freshly cracked pepper and chopped chives before serving.