Combine the salt, black pepper and garlic powder, rub it over the tri-tip and let the meat stand for 30 minutes.
Stir the tomatoes, white onion, red wine vinegar and cumin together and refrigerate the salsa while the steak cooks.
Heat a two-zone grill to medium-high, brush the tri-tip with olive oil and sear it over direct heat for 4 minutes per side.
Move the roast to indirect heat, cover and cook for 20 to 28 minutes until the thickest part reaches 145°F.
Rest the tri-tip for at least 3 minutes, identify the two grain directions and slice each section thinly across its grain.
Pile the steak into the rolls and top each with 2 to 3 tablespoons drained tomato salsa.