Set a medium-sized pot or Dutch oven over medium heat. Add the oil, followed by the garlic, shallot, and ginger. Sprinkle with sea salt. Cook, stirring often, 3 minutes. Add curry paste and cook 3 minutes more. Toss in bok choy, sauté 1 minute. Pour in coconut water and broth, and add lemongrass. Bring soup to a boil then turn heat down to a gentle simmer. Cook 15 - 20 minutes. Taste, and add sea salt as needed.