01 - Combine all marinade ingredients in a bowl. Add beef cubes and toss to coat thoroughly. Cover and refrigerate for a minimum of 1 hour, up to 8 hours for enhanced flavor.
02 - Heat grill or broiler to medium-high. Soak wooden skewers in water for 30 minutes if using to prevent burning.
03 - Toss bell peppers, mushrooms, and red onion with 2 tablespoons olive oil, salt, and pepper in a large bowl.
04 - Alternately thread marinated beef, bell peppers, mushrooms, and red onion onto skewers, ensuring even distribution.
05 - Cook kebabs on the grill for 10 to 15 minutes, turning occasionally, until beef reaches desired doneness and vegetables are tender and lightly charred.
06 - Allow kebabs to rest for 2 minutes before serving hot.