For best results, salt and tightly wrap roast in cellophane to cure overnight and bring roast to room temperature before cooking. This will help ensure even cooking.

Preheat oven to 250 degrees F. Place a cast iron skillet in the oven to warm. 

In a small food processor or spice grinder,  add the garlic powder, onion flakes, oregano, rosemary and thyme. Pulse to a fine powder. 

If you did not cure roast overnight, rub sirloin with salt and half the avocado oil.  

Carefully remove the preheated pan from the oven. Add the other half of avocado oil and place on the stove at medium-high heat. Add the roast and sear for 3-4 minutes on each side. 

Carefully rub the herb mixture over the meat and insert an oven-safe meat thermometer. Transfer pan with roast to the oven. Roast  for 1 hour 20 minutes or until the roast reaches an internal temperature of 120F for medium-rare, or 130F for medium. (Time will vary based on size of roast)

Once the roast has reached desired doneness, turn off the oven and let the roast rest inside the oven, 30 minutes, or until the internal temperature rises to your final desired temperature (around 130F for medium-rare, or 140F for medium). Do not open the oven door.

Remove from oven and transfer to a cutting board. Tent with foil and let rest for 15 minutes. 

Slice on the bias and serve with au jus.