Cut a horizontal slit in pork tenderloin, leaving the halves attached. Rub tenderloin with olive oil.

Insert garlic into the slit and onto the fatty part of the pork. Press thyme and rosemary into the slit. Sprinkle tenderloin with salt and pepper.

Preheat an outdoor grill for medium-high heat.

Lightly oil the grill grate. Place pork on the grill. Cook approximately 1 hour, turning every 15 minutes, to a minimum internal temperature of 145 degrees F (63 degrees C).