Preheat your oven to 350°F.
In a small bowl, mix together garlic powder, onion powder, smoked paprika, black pepper, kosher salt, rosemary, and thyme.
Rub the tri tip with olive oil, then coat evenly with the spice mixture. Let the coated roast rest at room temperature for 15 minutes before cooking.
Heat the oil in a cast-iron skillet over medium-high heat. Once hot, sear the tri tip on all sides until browned, about 3-4 minutes per side. Insert an oven-safe meat thermometer into the thickest part of the roast.
Transfer the skillet with the tri tip into the preheated oven and cook until it has reached an internal temp of 130F-135F for medium-rare, about 27-32 minutes depending on the thickness. Keep in mind that it will rise about 5 degrees as it rests. For medium, allow it to continue cooking until it reaches 140-145F. For other levels of doneness, see notes.* Keep in mind that it is recommended to allow it to reach an internal temperature of 145F, but individual preferences vary.
Once it’s finished cooking, remove it from the oven, tent it with aluminum foil and let the roast rest for 10 minutes before slicing. This allows the juices to redistribute and gives time for the carryover cooking to complete.
Slice against the grain and serve.