Heat a cast iron skillet. Add olive oil. Sear both sides of roast for about 3 minutes on each side. Transfer onto metal rack placed on a roasting pan.
Place tri-color peppercorns into a plastic sandwich bag. Crush peppercorns with a meat pounder or rolling pin. Transfer to a bowl. Mix with kosher salt, dried rosemary, thyme, and garlic.
Preheat oven to 500°F (260°C).
Pat peppercorn and salt mixture all over meat.
Place in oven and roast for 20 minutes at 500°F (260°C), then reduce heat to 300°F (150°C) and roast for another 30 to 35 minutes or until a meat thermometer registers 135°F - 140°F (57°C - 60°C) for medium rare and 145°F (63°C) for medium.
Remove from oven and cover with a piece of aluminum foil. Let it rest for 15 to 20 minutes for slicing.