Whisk together lemon juice, olive oil, brown sugar, soy sauce, salt, Worcestershire sauce, black pepper, garlic, and chili powder in a small bowl.
Place trip-tip in a large resealable bag and pour in the marinade. Seal bag, removing as much air as possible. Place in refrigerator and marinate 6-8 hours. Or overnight for optimal flavor.
In a medium bowl add sliced peppers and onions add olive oil salt and pepper and toss until combined. Set aside.
Heat a gas or charcoal grill on medium-high heat. Remove beef from marinade and place directly over coals for 5-6minutes then flip and cook another 5-6 minutes or until you get a good sear. Move Tri-Tip to indirect heat and cook covered for 25-30 minutes. Then check the temp with a meat thermometer, grill to desired doneness 120°F for rare, 130°F for medium-rare, and 140°F for medium
Let meat rest 10-15 minutes. Slice into thin slices against the grain.
While the meat is resting, place a cast-iron skillet directly over hot coals, and cook until soft about 10 minutes stirring every so often.
Notes
If you don't have a cast-iron skillet to use on the grill for the onions and peppers. Heat a skillet on medium-high heat on the stove and cook until soft.