How to Make It
Preheat the oven to 350°. Set the beets in a baking dish. Squeeze the juice from the orange halves over the beets; add the orange halves and ginger to the dish. Drizzle the beets with the oil and season with salt and pepper. Cover tightly with foil and bake for 1 hour and 15 minutes, until the beets are tender. Let cool, then peel and cut into 1-inch pieces. Leave the oven on.
Meanwhile, toast the nuts in a pie plate until golden, about 10 minutes. Let cool, then coarsely chop. In a bowl, cover the wakame with cold water and let stand until rehydrated, about 5 minutes; drain. Rinse under cold water, then drain again.
In a large bowl, toss the beets with the wakame, toasted nuts, vinegar, sesame oil, onion and scallions. Season the poke with salt and pepper. Refrigerate until slightly chilled, about 15 minutes.
In another bowl, mash the avocados with the lemon juice, wasabi powder and 1 tablespoon of water. Season the avocado with salt and pepper. Refrigerate until chilled, about 15 minutes.
To serve, mound the poke on plates and garnish with the golden beet, if using. Pass the avocado-wasabi mash at the table.