Heat the oven to 425º F and place a rack in the middle position.
Finely crush the cumin, coriander, and mustard seeds along with the turmeric and 1 teaspoon of the salt with a mortar and pestle. Place the cauliflower florets in a large mixing bowl and toss with 2 tablespoons of the coconut oil, then sprinkle in the spice mixture and combine well. (If you use your hands, you may want to glove up unless you want them bright yellow for a few days.)
Transfer the contents of the bowl to a half sheet pan and roast for 20 minutes, tossing half-way through.
Place a 5-6-quart heavy bottom pot or Dutch oven over medium heat for 2 minutes. Add the remaining coconut oil and 1/4 cup of the peanuts. Cook, stirring constantly, until browned and toasty 2-3 minutes. Add the onion and remaining 1/2 teaspoon salt and sweat until translucent, about 3 minutes. Add the ginger, garlic, and Thai chilis and cook 1 more minute.
Boost the heat to medium-high and add the roasted cauliflower, coconut milk, and coconut water. Bring to a simmer, cover with a lid, reduce to low, and cook for 10 minutes.
Pour the soup, a ladle at a time, into your blender's carafe. Fill the carafe no more than half full, which means you will probably need to do this in two batches, depending of course on how large your carafe is. Close the lid but remove the center feeder cap and place a folded kitchen towel over the top. This will allow some steam to escape, preventing the soup from exploding all over the kitchen. Start your blender on the lowest setting, or quickly pulse a few times, then gradually increase to high speed and blend for 1 minute.
Return the soup to the pot and stir in the lime juice. Keep warm on low heat until ready to serve.
For the gremolata: mix the cilantro, garlic, and lime zest in a small bowl and set aside.Serve in bowls topped with the gremolata and a sprinkling of the roasted peanuts, if desired.