Trim silver skin off the trip tip but leave some of the fat.
Massage the meat with the rub until fully covered and let rest at room temperature for 1 hour.
Prepare a charcoal grill or gas grill to high. Place tri-tip on grill and sear one side well, 6 to 7 minutes making sure it doesn’t burn. Rotate the tri-tip and sear other side for about the same time. Reduce heat to medium-high or move the meat to a part of the grill that’s not over direct flames. Turn meat again and cook another 8 to 10 minutes. Flip and cook again for an additional 5-6 minutes. A 2-pound roast will need about 20 to 25 minutes total cooking time. Cook until an instant read thermometer reads 120°F for a rare roast, 130°F for medium-rare and 140°F for medium.
Remove from the grill, let rest on a cutting board 30 minutes for the juice to redistribute and for it to slightly cool.
Arrange tomato slices, cucumber slices, and basil along a serving board. Drizzle tomatoes and cucumbers very lightly with vinegar. Drizzle oil over everything and season liberally with sea salt and ground pepper To serve, slice against the grain. Serve next to tomatoes and cucumbers.