Preheat your oven to 375°F (190°C).
Rinse the Cornish hens under cold water and pat dry with paper towels.
In a small bowl, mix olive oil, garlic, rosemary, thyme, salt, and pepper.
Rub the mixture all over the hens, including under the skin.
Stuff the cavity of each hen with half a lemon.
Place the hens breast-side up in a roasting pan.
Pour chicken broth into the pan.
Surround the hens with chopped seasonal vegetables.
Roast for about 1 hour, basting halfway through.
Check the internal temperature; it should reach 165°F (75°C) when done.