Add 4 tablespoon tahini to a medium mixing bowl
While whisking, slowly drizzle in 1–2 tablespoon water; keep whisking until mixture seizes up and thickens
Continue adding water 1 tablespoon at a time, whisking between each addition, until sauce loosens to a thick, creamy texture (about 4–6 tablespoon total)
Whisk in 2 teaspoon balsamic vinegar
Add ½ avocado (diced or scooped) and mash into the tahini with a whisk or fork until smooth
Season with kosher salt and lemon juice to taste
Adjust thickness with a bit more water or tahini if needed
Garnish with sesame seeds if using and serve