In a mixing bowl, whisk together ranch packet, garlic powder, minced garlic, soy sauce, mustard, oil, and lemon juice. Place pork in a large sealable bag, and pour in the marinade. Push out the air, and seal. Move the pork around in the bag so it is coated in the marinade. Place in fridge 6-8 hours.
Pre-heat oven to 350°F. Heat the olive oil over medium-high heat in an oven safe skillet. Brown pork tenderloin on all sides.
Place the skillet in the oven and cook for 20-25 minutes (flipping halfway) or until the pork registers 155-160 degrees. Remove from the oven, tent with foil to keep warm while the pork rest for about 5 minutes.
Slice and serve.
Notes
The pork tenderloin can be grilled in place of roasting.