Combine the 1 cup full fat plain yogurt, 1 1/2 tablespoons mayonnaise, 1/4 teaspoon salt, 1/4 teaspoon black pepper, 1/2 teaspoon garlic powder, 1/4 teaspoon chilli powder, 2-3 teaspoons lemon juice, and 2 tablespoons tahini in a bowl and whisk together well.
If the sauce seizes up and clumps together (specifically after whisking in the tahini), simply continue to whisk and add a few drops of water if required. It will become a smooth sauce.
Store in an airtight container for 1-2 weeks. Drizzle on Shawarma!
Notes
You can adjust the amount of mayonnaise in this recipe to your liking. More will result in a more decadent sauce.
You can skip the tahini if you don't have it.
If you like a stronger garlic flavour, add freshly crushed garlic.