To make the dressing, whisk together the Dijon, maple and vinegar. Drizzle in the olive oil, whisking to combine. Season to taste with sea salt and pepper. Set aside.
To make the millet, place the millet in a small saucepan on low and allow to dry toast for a few minutes. Add the water and bring to a boil, then lower heat to a simmer. Cover and allow to cook, simmering for 15 minutes. Take off the burner and let sit, covered, for 5 minutes. Toss the cooked millet with some of the dressing and set aside. This can be done up to a day in advance. The longer the millet marinates in the dressing, the better. Store in the refrigerator and allow to come to room temperature before serving.
Toss the squash, grapes and shallot in a large bowl with olive oil, sea salt and pepper. Spread onto a foil-lined half sheet pan and roast in the oven for 20 minutes until the squash is fork tender.
To assemble, plate some of the squash rings on a platter or plate, layering with the millet, greens and grapes. Drizzle any pan drippings and spoon a little more dressing on top. Garnish with walnuts and sea salt. Serve at room temperature.
