Prepare the tri-tip: Pat the tri-tip roast dry with paper towels to remove any excess moisture.
- Make the marinade or rub: Combine olive oil, soy sauce, garlic, rosemary, brown sugar, paprika, black pepper, salt, onion powder, cumin, and red pepper flakes in a small bowl. Mix well.
- Marinate the meat: Rub the seasoning mixture all over the tri-tip. For best results, marinate for at least 30 minutes, or up to 2 hours. You can also marinate overnight in the refrigerator.
- Preheat the grill: Preheat your grill to medium-high heat (400-450°F or 200-230°C). For a charcoal grill, use indirect heat by placing coals to one side.
- Grill the tri-tip: Sear the tri-tip on the hot side of the grill for 3-4 minutes on each side until a nice brown crust forms. Then, move it to the cooler side of the grill and cook for another 20-30 minutes, depending on your desired doneness (use a meat thermometer for accuracy).
- Rest the meat: After grilling, remove the tri-tip from the grill and let it rest for 10 minutes to allow the juices to redistribute.
- Slice and serve: Slice the tri-tip thinly against the grain and serve immediately with your favorite sides.