Preheat oven to 425 degrees F.
Make the pickled onions. Combine the boiling water with rice vinegar, sugar, mustard seeds, and salt, stirring to dissolved. Add the sliced scallions and let sit for 30 minutes.
Meanwhile, make the coconut rice. Wash the jasmine rice until the water runs clear. Drain the rice and combine it with the coconut milk, water, and salt in a large pot. Bring to a boil over high heat, cover the pot, and reduce the heat to low. Continue to simmer for 15-20 minutes or until the liquid is absorbed and the rice is tender. Fluff the rice with a fork and keep warm.
Drizzle 2 tablespoon oil on the sea bass and season with salt and pepper. Lay the fish on a sheet pan and roast in the oven for 12-15 minutes or until the fish flakes easily. Remove from the oven.
Prepare the miso chili lime sauce. Heat 1 tablespoon oil in a large saute pan over medium-high heat. Add the onion, garlic, and Thai chilies and saute until softened, about 3-4 minutes. Add the miso, stirring to combine.
Add the coconut cream, mirin, and sugar to the pan. Bring to a boil, reduce heat to low and simmer for 10 minutes, stirring frequently. Add the chili oil, lime zest, and juice. Season the sauce with salt and pepper and keep warm.
Heat 1 tablespoon oil in a large saute pan. Cook the baby bok choy until seared and the thick stems are softened, about 5-6 minutes. Season with salt and pepper.
Plate the fish on plates and spoon the miso chili lime sauce on top. Top with the pickled onions and serve with the coconut rice and seared bok choy.