Read through entire recipe before getting started.
Wash and dry all produce. Preheat oven to 375 degrees.
Remove peel from onion, cut in half, and then thinly slice into half moons. Remove ends from carrots, cut into half and then half again to form quarters. Cut acorn squash in half, scoop out seeds, and then slice each half into 1/2 inch moons. Cut lemon into 1/4 inch slices. Remove chicken from package and pat dry.
In a large Dutch oven or pot, heat 2 Tablespoons olive oil. Season chicken with salt and pepper. Add 2 chicken quarters, skin-side down and sear over high heat undisturbed until skin is golden brown and crispy, 3-4 minutes. Flip and repeat on other side for 3-4 more minutes. Transfer to a plate and repeat with remaining chicken.
Add onion to pot and cook, stirring occasionally, until tender and beginning to brown. Add mustard and cook, stirring, until its oils begin to separate, 2-3 minutes. Add granulated garlic, dried herbs, and 1 cup water to deglaze the pan and cook, scraping up any brown bits from the bottom.
Add carrots, acorn squash, and lemon to the pot and stir to coat with sauce. Return chicken to pot, nestling it in with the vegetables.
Cover and transfer to oven. Bake for 40-45 minutes, basting every 10 minutes until chicken is fully cooked and vegetables are tender. Remove from oven, divide chicken and vegetables between plates and drizzle with mustard jus from pan. Enjoy!