Place the cashews with soaking water, lemon juice, chickpea flour,cayenne, tomatoes, ginger and curry powder into a blender and zap until you have a very smooth paste.
Heat the oil in a saucepan and add the mustard seeds. When they sputter, add the cumin seeds and then the fennel and stir quickly.
Turn off the heat, add a cup of water and the cashew-tomato paste to the pan, and return to heat. Stir well to mix.
Heat the sauce over medium heat until it simmers. Turn the heat to low and cook 15 minutes. The sauce will thicken as it cooks.
Add the baked tofu and heat the sauce through. Turn off heat and sprinkle on the coriander leaves.
Serve hot with rice or rotis.