Soak the chick peas overnight in water. Drain, put into a pan, cover with water bring and boil for 10 minutes. Then simmer for around 1 ½ hours until the chick peas are soft.
Place in a food processor with the tahini, lemon juice, garlic, cumin and bicarbonate of soda. Add 4 tbsp of olive oil to start. Blend until thick -you will probably need to add more olive oil until you get the desired texture. You can also add a little water.
Add plenty of salt and pepper.
Spread the bread thickly with hummus and top with beansprouts, watercress and the tomato and cucumber slices.