In a small bowl, combine the salt, pepper, garlic powder, oregano, onion powder, smoked paprika and chili powder. Pat the roast dry thoroughly and rub all over with the spice mixture. Let stand at room temperature for 30 to 45 minutes.
Preheat the oven to 400ºF; place a large cast iron or other heavy bottom skillet in the oven as it preheats.
Transfer the skillet to the stove; place over medium-high heat. Add the oil and swirl to coat the bottom of the skillet. Place the tri-tip in the skillet and cook undisturbed until seared on one side, about 3 minutes. Carefully flip the tri-tip. Transfer the skillet to the oven and cook until a meat thermometer stuck into the thickest part reads 120ºF for medium rare, 20 to 25 minutes (start checking after 15).
Transfer the roast to a cutting board. Tent with foil and let rest for at least 5 minutes. Thinly slice against the grain and serve. (Note: The grain changes direction on a tri-tip, usually about halfway across the roast. Look closely to find the spot. Cut the roast into 2 pieces and slice each against the grain.)