Preheat oven to 400*F.
In a large bowl, combine the carrots, shallots, squash, Brussels sprouts, and garlic. Drizzle 2 tbls. of the olive oil, and season with salt and pepper. Toss to coat. Pour vegetables onto a sheet tray and roast in the oven for 30 minutes, tossing once, halfway through.
Meanwhile, prepare the lentils by putting them into a small saucepan and covering with water by 2 inches. Add the onion and bay leaf. Bring to a boil, then simmer covered for 20 minutes, or until tender. Drain and discard the onion, season with salt and pepper and set aside.
Once the veggies are finished roasting, remove the garlic. Peel and mash the garlic in a small bowl, combine with the remaining 4 tbls. of olive oil, apple cider vinegar, and Dijon mustard, and whisk into a vinaigrette. Toss the lentils with the vinaigrette, fold in the arugula or spinach leaves, and then top with roasted vegetables to serve.