Combine the tahini and lemon juice in a food processor and process until pale and fluffy, about 30 seconds.

Add the drained beans, garlic, salt, and cumin. Process 1 minute, scraping down the sides once.

With the motor running, slowly stream in the olive oil, then the cold water. Blend until glossy and smooth, about 45 seconds.

Transfer to a bowl, swirl with a spoon, and drizzle with olive oil. Finish with smoked paprika or sumac and serve.