Combine chili powder, garlic powder, cumin, oregano, onion powder, salt and pepper in a small bowl. Place tri tip in a large baking dish. Sprinkle all over with spice mix, rubbing all of it all over the steak. Cover and let stand at room temperature for at least 30 minutes or up to 1 hour.
Heat oven to 425ºF. Place a cast iron skillet in the oven as it heats. When hot, place skillet on stovetop over high heat. Add oil; swirl to coat skillet. Add tri tip and sear until browned all over, turning occasionally, about 3 to 4 minutes.
Transfer skillet to oven and cook until an instant-read thermometer stuck into thickest part of meat reaches 120 to 125ºF, about 12 to 15 minutes. Remove to a cutting board, tent with foil and let rest for at least 10 minutes. Slice against the grain and serve with salsa.