In a medium bowl, whisk to combine all of the marinade ingredients. Set aside.
Cut the beef into 1- to 2-inch cubes. Cut the onion and peppers into 2-inch pieces. Add the meat and vegetables to the marinade in the bowl and turn the pieces to fully coat them. Cover and refrigerate for at least 2 hours and up to 8 hours.
When you’re ready to grill, coat the grill grates lightly with oil and heat the grill on medium high.
Thread 8 metal skewers with the meat, onion, and peppers; discard the marinade.
Grill the kebabs, turning them halfway through cooking, about 12 minutes total. Remove the skewers from the grill. Before serving, push the meat and vegetables off the skewers onto a platter and drizzle with olive oil.