Preheat oven to 425ºF. Melt butter in medium saucepan over medium heat. Add millet and stir to coat. Cook, stirring, until golden in spots and toasty-smelling. Add water and salt, stir, cover, and bring to a boil. Reduce heat to low and simmer until very tender, about 15 minutes. Remove from heat and let stand 10 minutes before fluffing with a fork.
Peel root vegetables and cut into equal size pieces. Toss with olive oil and salt, then spread in a single layer on a parchment-lined baking sheet and roast until tender and caramelized, about 25 minutes.
Whisk together all ingredients for dressing. Divide millet between 4 bowls and top with roasted vegetables, kale, beet and pumpkin seeds. Drizzle with dressing and serve.