Place kosher salt and rosemary in a spice grinder or food processor and blitz until very fine. Transfer to a small bowl and mix in the remaining ingredients for form a wet rub. This makes 3+ tablespoons.
Remove meat from fridge an hour (or two) before grilling. Rub with wet rub using 1 tablespoon per pound of meat. Cover with plastic wrap and marinate in the refrigerator for at least 4 hours, better if left over night. Remove meat from fridge 1 hour before grilling
Set up grill for both direct grilling over medium-high heat and also a zone for indirect heat. Sear meat fat side up until well-marked and a little charred. Turn and repeat on the other side. Move to the indirect area, cover grill and and grill until an instant-read thermometer inserted into the thickest part registers 130 degrees F, about 30 minutes. Tri tip is best served rare to medium rare... medium should be your upper most limit of doneness; overcooking can dry the meat, leaving it tough and unappetizing.
Transfer meat to a cutting board and let rest 20 minutes before slicing. Slice thinly on the bias and across the grain.
Slather toasted rolls with smashed avocado and build an amazing sandwich!
Recipe by Grilling Outdoor Recipes powered by Bull Outdoor Products at https://blog.bullbbq.com/your-game-day-sandwich-california-tri-tip-with-avocado/