In a large non-stick pan, heat some oil on medium heat, Add in the mustard seeds and allow them to fry for 30 seconds. You should start to see them sizzle and start popping. Immediately add in the finely grated ginger, minced garlic, chilli, and chopped onions. Cook for a few minutes until fragrant and the onions start to become translucent. While the mixture is cooking, add all the Sauce ingredients into a blender. Once the onions start to become translucent, turn off the heat, and add all the contents of the pan into the blender containing the Sauce ingredients. Blend on high until completely pureed into a smooth sauce. Pour the sauce back into the pan, add all the Spices and mix to combine.
Heat the sauce to a simmer and cook uncovered for 10-15 minutes on medium-low heat. Add all the cauliflower florets into the sauce, toss, and cook, covered, for about 10 minutes on low heat or until the cauliflower florets are cooked and tender yet able to keep shape. Remove the cover and cook again on medium heat, stirring occasionally, for up to about 10-15 minutes. Add the ground cashew nut and finish with coriander, serve with rice.