Makes 6 Servings
Mix together all the ingredients in the spice rub.
Rub the Tri-Tip liberally with spice mixture and allow it to marinate overnight. Remove it from the fridge for an hour before cooking.
Place onions, butter, a pinch of salt and pepper and the sugar in a pan over medium heat. Cover the pan and cook for 5 minutes.
Remove the lid and stir in the onions. Turn the heat up to medium high and cook until the onions are caramelized.
Deglaze with the cider and vinegar. Remove from heat and reserve for later use.
Place the Tri-Tip on your grill over medium heat. Allow the meat to cook on one side for 10 minutes before flipping over and allowing the other side to cook for an additional 10 minutes.
Remove from the heat and allow the meat to rest for an additional 10 minutes.
Slice against the grain and serve with the onion relish.