Season tri-tip. Pour 2 tablespoons of olive oil on tri-tip on both sides. Combine salt, pepper, garlic powder, onion powder, paprika, and cayenne. Sprinkle seasonings over tri-tip on both sides and let sit at room temperature for 30 minutes.
Preheat oven to 400 degrees F.
Whisk together remaining 2 tablespoons olive oil with 2 tablespoons red wine vinegar.
Place tri-tip on roasting rack. Roast for 10 minutes and remove from the oven. Baste the tri-tip with olive oil and vinegar mixture. Continue to roast for 15-30 minutes or until internal temperature reads 130-135 degrees F for medium-rare. Remove from heat and loosely tent with foil. Let rest for 15 minutes.
Prepare the chimichurri while tri-tip is roasting. Combine parsley, olive oil, lemon juice, shallot, garlic, lemon zest, and red pepper flakes in a medium bowl. Season with salt and pepper. Let sit for 10 minutes to allow flavors to meld together.
Slice tri-tip against the grain and serve with chimichurri.
Notes
You can prepare the chimichurri up to 3 days in advance.Temperature guideline for tritip: Rare: 120-130 degrees F, Medium-Rare: 130-140 degrees F, Medium: 140-150 degrees F, Medium-Well: 150-160 degrees F