Rice the cauliflower: Cut the cauliflower roughly into florets. Place the florets in a food processor and chop until the cauliflower is roughly the size of grains of rice. You may need to scrape down the cauliflower on the sides of the food processor in the middle of chopping. Also, I recommend chopping using pulses to avoid over-processing the cauliflower. You do not want to turn the cauliflower into a purée.
Fry the mustard seeds: Heat ½ tbsp oil in a large pan over medium heat. Once the oil is hot, add the mustard seeds and cover the pan immediately. Once the seeds stop spattering, remove the lid (you won’t need it anymore). Be sure to keep an eye on the mustard seeds to avoid burning them. Once the mustard seeds are fried, turn the heat down to medium-low, and add the butter.
Sauté: When the butter starts to sizzle, add the finely chopped onion, cook for 1 minute. Then add the cauliflower rice, turmeric, ginger, salt, and black pepper. Cook for 10 minutes, stirring occasionally to avoid burning and to allow the cauliflower to cook evenly. The cauliflower should become somewhat toasted.
Chop: While the cauliflower is cooking, chop the cashews, herbs, and olives. The parsley should be finely chopped for the best texture.
Assemble & serve: When the cauliflower is done cooking, stir in the lemon juice and top with the chopped ingredients. Serve right away.