Start by cutting the tri-tip steak into 1½-inch cubes, combine soy sauce, brown sugar, minced garlic, rice vinegar, and sesame oil in a large bowl. Reserve one-third of this marinade for later basting. Coat the steak in the marinade and refrigerate for at least 4 hours or overnight.

Once marinated, cut pineapple, red bell peppers, and sweet onion into 1½-inch chunks. Thread skewers by alternating marinated steak, pineapple, bell peppers, and onion, aiming for 4-5 pieces per skewer.

For the basting sauce, mix reserved marinade with ketchup and honey in a small bowl until smooth.

Preheat grill to medium heat (around 350°F). Grill skewers for about 15 minutes, turning every 2-3 minutes, and baste generously during the last few turns.

Check doneness with a meat thermometer. The internal temperature should reach 145-150°F for medium doneness. Remove from grill and let rest.

Transfer skewers to a platter and garnish with sesame seeds and chopped green onions. Serve alongside your favorite sides.