Pre-heat the oven to 400 degrees F with a 12 inch cast iron skillet inside.
Cut the onion into quarters.
Place the potatoes, carrots, and onions in a bowl with 1 tablespoon of the olive oil. Toss well to coat.
Rinse the hens and pat dry with paper towels.
In a small bowl, mix together the salt, thyme, oregano, and ground black pepper and set aside.
Rub 1 tablespoon of olive oil, divided evenly, over the top and bottom of each hen.
Next rub the jarred minced garlic, divided evenly, over the top and bottom of each hen.
Sprinkle half of the herb mixture (reserve the rest), divided evenly, all over the top and bottom of each hen.
Remove the cast iron skillet from the oven and brush with olive oil.
Place the hens into the center of the pan, breast side up. It will make a lovely sizzling sound. Be very careful not to touch the pan and get burned.
Add the potatoes, carrots, and onions to the pan around the hens.
Sprinkle the reserved seasonings over the veggies.
Bake for 55 - 60 minutes or until the internal temperature reaches 165 degrees F.
Carefully transfer the hens and vegetables to serving plates and enjoy.