To help vegetables brown evenly, give them an occasional stir while they're roasting, and slice denser veggies (like carrots), into smaller pieces than you would lighter ones (like Brussels sprouts).
Preheat oven to 400°F with racks in upper and lower thirds. Line 2 rimmed baking sheets with parchment.
In a large bowl, toss vegetables with olive oil and salt. Divide vegetables evenly between baking sheets, spreading them out in a single layer. Roast, stirring occasionally and switching baking sheets halfway through, until tender and very browned, 30 to 40 minutes.
In a small bowl, whisk together sesame oil, rice vinegar, miso, soy sauce and honey.
Remove vegetables from oven and transfer to a serving bowl. Immediately toss with miso vinaigrette. Scatter sesame seeds and scallions on top and serve.