Make Marinade: To a gallon-sized freezer bag, add steak, garlic, soy sauce, oil, Worcestershire, honey, onion powder, pepper, and red pepper flakes. Press air out, seal, and toss to combine.
Marinate Steak: Place the bag in the refrigerator for at least 30 minutes and up to 8 hours to marinate. Tip: Set the bag in a dish in case there are any leaks. Meanwhile, if using wooden skewers, soak them in water for at least 30 minutes.
Prep the Grill: Clean and preheat a grill or grill pan to medium heat (around 350°-400°F).
Build Kabobs: Build the kabobs in a 9x13-inch baking dish to contain the mess. Thread a piece of onion, bell pepper, and beef onto the skewers, repeating until the skewer is mostly filled. (You’ll end up with about 3 pieces of meat per skewer.) Leave a little space between each ingredient so they grill evenly. Pour the rest of the marinade over the kabobs to coat the veggies.
Grill Kabobs: Grill the kabobs, turning frequently, until the vegetables are tender and the beef is seared on all sides and cooked to desired doneness*, about 8-10 minutes. (Be sure to discard the marinade.) Let rest for 5 minutes.
*USDA recommends a safe minimum internal temperature of 145 degrees for beef.