01 - Whisk together olive oil, soy sauce, lemon juice, minced garlic, oregano, cumin, black pepper, paprika, and salt in a medium bowl to form a marinade.
02 - Add beef cubes to the marinade, toss to thoroughly coat, cover, and refrigerate for a minimum of 1 hour to allow flavors to develop.
03 - If using wooden skewers, soak them in water for 30 minutes to prevent burning during grilling.
04 - Alternate threading marinated beef, red, yellow, and green bell peppers, and red onion pieces onto the skewers evenly.
05 - Heat grill or grill pan over medium-high heat until hot and ready for cooking.
06 - Grill the skewers for 10 to 12 minutes, turning occasionally, until beef reaches desired doneness and vegetables develop light char marks.
07 - Remove skewers from the grill and allow them to rest for 3 minutes before serving to retain juices.