Chop the onion, put the chickpeas and onion in a large heavy saucepan, cover with water and bring to a boil. Cook for 1 hour, or until the chickpeas are very soft. (You could avoid this step by using canned chickpeas!). Drain, reserving 1 cup of the cooking liquid and leave to cool.
Chop the beet and put in a food processor, in batches if necessary. Add the chickpeas and onion mixture, tahini, garlic, lemon juice and cumin, and process until smooth. Slowly add the reserved cooking liquid and olive oil while the motor is running. Process until the mixture is thoroughly combined. Drizzle with a little olive oil and serve with pita bread and your favourite raw veggies!