Preheat oven to 450°. Cook black rice and wild rice in a large pot of boiling salted water until tender, 35–40 minutes; drain and rinse, shaking off as much water as possible. Spread out on a rimmed baking sheet and let cool.Meanwhile, toss squash with ¼ cup oil on another baking sheet; season with salt and pepper. Roast, tossing once, until golden brown and tender, 20–25 minutes; let cool.
Whisk vinegar, honey, and remaining ¼ cup oil in a large bowl. Add black rice and wild rice, squash, scallions, pomegranate seeds, microgreens, and pistachios; season with salt and pepper and toss to combine.