Add 2 tablespoons of olive oil or other cooking oil to a large, heavy ovenproof pan. On stovetop, heat on high until pan is very hot, then add tri-tip, fat side down. Turn heat to medium-high and sear roast for about 4 minutes.
Turn the roast and put it in the oven. Cook it for about 10 minutes a pound, checking with an instant-read thermometer until it reaches 130 degrees for medium-rare or 120-125 for rare.