In a medium saucepan, bring rice, 1/2 tsp. salt, and 4 cups water to a boil. Cover, reduce heat to a simmer, and cook until rice is tender to the bite, about 50 minutes. Remove rice from heat, uncover, and fluff with a fork.
Meanwhile, cut nori into 1/4-in. strips and set aside. Slice green onions crosswise (including green parts) and set aside.
Preheat broiler. Rub a baking sheet with oil. Put fish on sheet and turn over to oil both sides. Sprinkle with remaining 1/2 tsp. salt. Broil 3 to 4 in. away from broiler until cooked through (flesh flakes easily and is opaque in the center), about 5 minutes. Transfer fish to a plate and set aside.
When rice is cooked, bring 8 cups water to a boil. In a large teapot, measuring cup, or pitcher, pour water over tea bags. Let steep 5 minutes.
Meanwhile, put 1 cup rice in each of 4 large soup bowls. Place 1/2 fish fillet on each bed of rice. Pour 2 cups hot tea over each. Sprinkle with green onion and black sesame seeds. Serve immediately, with bowls of nori, tamari, and sesame oil on the side if you like.
Note: Nutrition analysis is per serving.