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.