Prepare the marinade. In a large mixing bowl combine olive oil, Dijon style mustard, maple syrup, minced garlic, salt, pepper, and dried thyme or rosemary. Stir until smooth.
Season the chicken. Pat the chicken thighs dry with paper towels. Add them to the bowl and turn each piece so it is coated in the maple mustard marinade. Set the bowl aside at room temperature while you prepare the vegetables.
Heat the oven. Turn the oven on to about 400 degrees Fahrenheit. Line a large rimmed sheet pan with parchment or lightly oil it.
Prep the vegetables. Add the sweet potato cubes, Brussels sprouts halves, red onion wedges, and carrot slices to the sheet pan. Drizzle with the olive oil and sprinkle with salt and pepper. Toss on the pan until all pieces have a thin coat of oil and seasoning, then spread them into a single layer.
Add the chicken. Move some vegetables toward the edges of the sheet pan to make spaces for the chicken. Place the marinated chicken thighs in those spaces in one layer. Pour any extra marinade from the bowl over the chicken and nearby vegetables.
Roast. Place the sheet pan on the middle rack of the hot oven. Roast for about 20 minutes without turning.
Cook the quinoa. While the sheet pan roasts, rinse the quinoa in a fine mesh strainer under cool water. Put the rinsed quinoa in a medium saucepan with the water or broth and salt. Bring to a gentle simmer over medium heat, then reduce the heat to low, cover with a lid, and cook for about 15 minutes until most liquid is absorbed. Turn off the heat and let it rest covered for 5 minutes. Fluff gently with a fork.
Finish roasting. After about 20 minutes, pull the sheet pan out and gently turn the sweet potatoes, Brussels sprouts, and carrots with a spatula so more sides can brown. Spoon some of the pan juices over the chicken. Return the pan to the oven and roast for another 10 to 15 minutes, until the chicken is cooked through and the vegetables are tender with light browning.
Rest. Remove the sheet pan from the oven and let the chicken and vegetables rest for about 10 minutes so juices settle and steam lessens. Taste the quinoa and adjust salt if needed.
Assemble the bowls. Set four meal prep containers on the counter. Divide the quinoa evenly among them to form a base. Place one or two chicken thighs into each container. Spoon roasted vegetables into each bowl, sharing the sweet potatoes, Brussels sprouts, carrots, and onions fairly.
Garnish. Sprinkle chopped parsley or cilantro over the bowls. Add pumpkin seeds and dried cranberries if you like extra crunch and a touch of sweetness. Let bowls cool until just warm, then seal and refrigerate.
Serve. For eating, reheat one container until hot all the way through. Serve as is, or slide the contents onto a plate and finish with a squeeze of lemon juice or a small spoon of yogurt if you enjoy a creamy touch.