Heat a saucepan and add the water - 'fry' the onion, garlic and red pepper for a couple of minutes until they start to soften, stirring continuously. Add a touch more water if you feel you need to.
Add the mushrooms, tomatoes, kidney beans, chickpeas, herbs and stock. Stir and bring to the boil.
Mix the cornflour with a little water to make a smooth paste and stir into the stew to thicken the sauce. Simmer for 10 minutes.