Preheat your oven to 375°F (190°C).

In a bowl, mix together the softened butter, minced garlic, lemon zest, rosemary, thyme, garlic powder, salt, and black pepper to create the herb butter.

Pat the Cornish hens dry using paper towels.

Gently loosen the skin of the hens with your fingers and spread the herb butter mixture under the skin and over the top.

Drizzle olive oil over the hens and season the outside with additional salt and pepper.

Arrange the hens in a roasting pan, breast side up, and sprinkle any remaining herbs on top or around them.

Place the roasting pan in the preheated oven and roast for about 1 hour or until the internal temperature reaches 165°F (75°C).

Once cooked, remove from the oven and let rest for about 10 minutes before serving.