Heat oven to 450ºF (232ºC) with racks set in middle and lowest positions.

Wrap each beet with aluminum foil and place on a small baking sheet; transfer to middle rack of oven and roast until beets can easily be pierced with paring knife, 45–60 minutes. Remove beets individually from oven as they finish; let cool.

Meanwhile, toss carrots with melted butter in a large bowl; season with ½ teaspoon salt and ¼ teaspoon pepper. 

Arrange carrots, cut-side down, in a single layer on a rimmed baking sheet. Transfer carrots to lowest rack in oven; roast until tender and cut sides are well browned, about 25 minutes. 

Meanwhile, combine oil and cumin seeds  in a small skillet over medium heat. Cook, stirring frequently until fragrant and toasty, 4–5 minutes. 

Off heat, add shallot and cook, stirring occasionally, until sizzling subsides, about 2 minutes. Let oil cool in pan (shallot will start to brown). Whisk in vinegar, maple syrup, and Dijon; season with salt and pepper.

Carefully open foil-wrapped beets; allow steam to escape away from you. Let cool slightly, then rub skins off using paper towels.

Cut beets into ½-inch thick wedges. Transfer beets and carrots to a large serving platter and drizzle with vinaigrette. Sprinkle with walnuts and parsley; serve immediately.