In a bowl, whisk together olive oil, soy sauce, lemon juice, garlic, smoked paprika, oregano, black pepper, salt, and cumin.
Add the beef cubes to the marinade, toss to coat, and let marinate for at least 30 minutes (or up to 4 hours for more flavor).
If using wooden skewers, soak them in water for 20 minutes to prevent burning.
Preheat the grill to medium-high heat.
Thread the marinated beef onto skewers, alternating with bell peppers, onion, and zucchini
Grill the skewers for about 10-12 minutes, turning occasionally, until the beef is cooked to your desired doneness.
Remove from heat and let rest for a few minutes before serving.
Serve with rice, pita bread, or a fresh salad.