Preheat your oven to 400°F (200°C).
In a large bowl, whisk together the balsamic vinegar, olive oil, honey, minced garlic, oregano, salt, and black pepper.
Add the chicken thighs to the bowl and coat them well with the marinade. Let them marinate for at least 30 minutes (or up to 2 hours in the refrigerator for more flavor).
In a large baking dish or sheet pan, arrange the halved baby potatoes, broccoli florets, sliced red bell pepper, and sliced onion. Drizzle with a little olive oil and season with salt and pepper. Toss to combine.
Place the marinated chicken thighs on top of the vegetables in the baking dish.
Pour any remaining marinade over the chicken and vegetables.
Bake in the preheated oven for 30-35 minutes, or until the chicken is cooked through (internal temperature of 165°F) and the vegetables are tender.
Remove from the oven and let it rest for 5 minutes before serving.