Preheat the oven to 425°F, and place one rack in the lower third position. Line a large, rimmed baking pan with foil, parchment paper, or a silicone mat (for easy clean-up).
Prepare the tahini sauce:
In a medium bowl, whisk together the tahini, lemon juice, vinegar, and miso until completely incorporated. The mixture will be a workable paste. Add the water one tablespoon at a time, whisking thoroughly, until the sauce is smooth and drips from the whisk when lifted from the bowl (you might not need the 4th tablespoon).
Let the tahini miso sauce rest while you prepare the vegetables. You can also make the sauce the day before, storing in the refrigerator. The sauce will thicken, but can be loosened with another tablespoon of very warm water.
Prepare the vegetables
In a large mixing bowl, toss the chopped vegetables with the olive oil to coat. Season with a big pinch or two of salt.
Spread the vegetables in the lined pan in a single layer. Roast in the oven for 30 to 40 minutes. Looked for golden edges on the sweet potatoes and carrots; you might need the upper end of the time range if you've sliced your veggies large.
Remove from oven and immediately sprinkle the za'atar spice and cilantro over the vegetables.
Serve the vegetables over the grains, and drizzle the tahini miso sauce on top
Try as best you can to slice the vegetables into similar sizes, so that they'll cook evenly. Also, feel free to substitute other oven-loving vegetables that you have on hand, such as winter squash, Brussels sprouts, fennel, etc.Roasted vegetables pair perfectly with leftover brown rice, quinoa, millet. If you're pressed for time, prepare a small pasta, such as orzo, which can be cooked while the vegetables are in the oven.