Cut onion into rings and put in a bowl with balsamic vinegar and pinch of salt and put aside.
Cut chilli in half and deseed. Chop spring onion into small pieces and put both into a bowl. Drain beans, rinse with water and dry with paper towel. Add it to the bowl with chilli and spring onion and add breadcrumbs.
Season and with your hands mix and squeeze all the ingredients. Divide in 3 and form into burgers and put into the fridge for 10 minutes.
In another bowl mix half lemon juice, 2 tbsp of extra virgin olive oil and yogurt. Season. Chop kale and along with rucola mix in. Put aside.
Heat 1 tsp of olive oil on a pan on medium heat. When the pan is hot, cook the burgers until they are nice and brown. You can also bake them in the owen.
Cut tomato and mozzarella into slices and cut the buns in half.
When the burgers are nearly ready, put on each of them a slice of mozzarella and let it melt.
Toast the buns. With a fork take some of the balsamic onion, on 1 side of the bun put a slice of tomato, put a burger on top of that, and on top of the burger put balsamic onion, then cover with other half of the bun. Serve with the kale salad.