Preheat your oven to 400°F (200°C).
In a small bowl, mix 2 tablespoons of olive oil, minced garlic, thyme, rosemary, salt, and black pepper to create a rub.
Pat the Cornish hens completely dry with paper towels. This ensures the skin gets crispy.
Rub the herb mixture evenly over the hens, getting under the skin of the breast if possible. Stuff the cavity with a lemon half if desired.
In a large roasting pan, toss the carrots, bell peppers, and onion wedges with the remaining 1 tablespoon of olive oil and a pinch of salt.
Pour the chicken broth into the bottom of the roasting pan.
Place the seasoned hens on top of the vegetables.
Roast in the preheated oven for 50 to 60 minutes, or until the skin is golden brown and an internal thermometer inserted into the thickest part of the thigh reads 165°F (74°C).
Remove from the oven and loosely tent with foil. Let the hens rest for 10 minutes before serving to lock in the juices.