Drain the onions and collect the stock. Halve some onions and put them aside. Pour the chickpeas into a sieve, rinse cold and drain well.
Fry the bacon in a pan without fat until crispy. Drain on kitchen paper. Finely mash onions, chickpeas, tomato paste, sour cream and oil with a hand blender. Season to taste with salt, pepper and 1-2 tbsp. onion stock.
Bacon is crumbling. Garnish hummus with halved onions, chilli flakes and bacon.