Put beans into a bowl; cover with water by about 2 inches. Soak overnight in the refrigerator. Drain beans; transfer to a medium saucepan. Cover with water by about 2 inches, and bring to a boil. Reduce heat; simmer, stirring occasionally, until tender, about 30 minutes, seasoning with 1 teaspoon salt halfway through and adding more water if needed to keep beans covered. Drain.
Rinse rice; drain. Transfer to a medium saucepan; add 3 1/4 cups cold water and a pinch of salt. Bring to a boil, stir once, and reduce heat. Simmer until water has been absorbed and rice is tender, 45 to 50 minutes. Remove from heat, and let stand 10 minutes.
For condiments, put seaweed into a small bowl; cover with cool water. Set aside until soft, 10 to 15 minutes. Drain.
Place the bottom basket of a large 2-tiered bamboo steamer in a wok or large pan filled with about 1-inch simmering water (the water should just reach to bottom of basket; alternatively, use 2 pans fitted with steamer inserts). Carefully place squash slices in a single layer in bottom basket. Cover, and steam 10 minutes. Place tofu in a single layer in top basket, and top with greens. Cover, and carefully set atop bottom basket; steam until greens and squash slices are tender, 7 to 8 minutes more.
Meanwhile, make the miso dressing: Process ginger, miso, tamari sauce, and 1/4 cup water in a food processor until smooth. With machine running, gradually add oil, and process until combined. Transfer to a small bowl; set aside.
Toss together daikon and vinegar in a bowl; set aside. Spoon rice into each of 4 large serving bowls, and arrange beans, greens, tofu, squash, and seaweed on top, dividing evenly. Top each bowl with about 1 tablespoon daikon mixture and 2 plums. Drizzle with dressing, and sprinkle with gomashio.