Heat the oil and fry the onion, celery, garlic and chilli, gently for 5 minutes until softened.
Remove from the heat. Allow to cool. Remove and discard the crusts from the bread and tear into pieces. Place in a food processor and blitz to crumbs. Add the cannellini beans and pulse together to form a smooth-ish purèe.
Add the red kidney beans and blitz again in short bursts until the red kidney beans are roughly chopped. Tip into a large mixing bowl.
Add the onion mixture, curry powder, and egg, and season well with salt and pepper.
Divide into six and shape into rounds. Chill for at least 30 minutes or until required.
When ready to serve shallow fry for 5 minutes each side until crisp and golden on the outside and piping hot in the middle. Serve in burger buns with tomato relish to accompany.
Notes The burgers can be stored in the refrigerator for up to 2 days. They also freeze well. Defrost before cooking.Nutrition information is approximate and for the burgers only. It is meant as a guideline only. (It does not include seasoning with salt and pepper.)