Preheat oven to 375°F.
Combine scallions, kosher salt, black pepper, and 1 tablespoon of cooking oil together.
Evenly press scallion mixture onto tri-tip roast.
Heat a skillet on medium-high heat, add remaining cooking oil to hot pan, and sear both sides of tri-tip for 3 minutes.
Remove from skillet and place on a roasting rack inserted on a baking sheet. Place in oven and roast for 45 minutes or until meat thermometer inserted into thickest part reads 125°F.
Remove from oven and let tri-tip roast rest for 10 minutes before slicing against the grain.