Preheat oven to 450°F. 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 1/4 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 1/4 cup oil in a large bowl. Add black rice and wild rice, squash, scallions, seeds, microgreens, ; season with salt and pepper and toss to combine. Top with huckleberries
DO AHEAD: Salad (without microgreens) can be made 4 hours ahead. Cover and chill.
Also try it with: any grain (except amaranth)