Heat the oil. Add the mustard, cumin, nigella, fenugreek and fennel seeds. When they sputter and start to darken, add the onions.
Saute the onions, stirring frequently, until they turn translucent.
Add the cayenne, paprika and salt. Stir to mix.
Add the cauliflower florets and mix well. Add the tofu. Mix.
Cover the pan and let the cauliflower florets cook until fairly tender but not mushy. Stir every few minutes to make sure the florets are cooking evenly.
Add salt and lemon juice. Mix thoroughly. Garnish with coriander leaves and serve hot.