Preheat the oven to 200°C.
Place the red onion, zucchini and pumpkin in a medium baking dish and drizzle with half of the olive oil. Toss to coat everything really well. Season with salt and pepper. Cook in the oven for 35-40 minutes.
Combine the honey, seeded mustard, the remaining olive oil, the garlic and white wine vinegar in a medium bowl. Season with salt and pepper. Add the chicken thighs and coat in the marinade.
Meanwhile, heat an oven proof medium frying pan over a medium high heat. Add the chicken and cook for 2 minutes on each side brushing with the remaining marinade as it cooks. Once the chicken is golden and sticky pour over any remaining marinade and transfer the pan to the oven for the final 8 minutes of the vegetable cooking time.
To serve, divide the chicken and vegetables between plates. Pour any excess honey and mustard sauce over the chicken and vegetables. Enjoy!