Beetroot burgers with herb feta sauce

Name: Beetroot burgers with herb feta sauce
Cook time: 1 h
Total time: 1 h
Ingredients: 1 onion chopped; 1 tsp cumin seeds; spray olive oil; 500g raw beetroot peeled and grated; 400g tin chickpeas rinsed and drained well; 1 egg beaten; 2 tbsp sesame seeds; 50g feta crumbled; chopped to make 1 tbsp dill, parsley or mint; 100ml fat-free yogurt; to serve frilly lettuce; to serve small burger buns; to serve finely sliced red onion