Add 1/4 cup tahini, 2 Tablespoons mayonnaise, 2 Tablespoons reduced sodium soy sauce, 1 clove garlic, 1/4 teaspoon onion powder, and 1/8 teaspoon paprika to a measuring cup or jar. Blend using an immersion blender, adding water 1 Tablespoon at a time to make a thick, smooth sauce. Refrigerate for at least 1 hour before using to let the flavors meld. Store any leftovers in an airtight jar or container in the fridge.