Cut the chicken breast and beef sirloin into uniform 1-inch cubes.
Chop the red bell pepper, red onion, and zucchini into 1-inch pieces suitable for skewering.
In a small bowl, whisk together the extra virgin olive oil, minced garlic, dried oregano, sea salt, black pepper, and lemon juice.
Place the meat and vegetables in a large bowl and toss with the marinade until thoroughly coated.
Thread the meat and vegetables onto skewers, alternating between chicken, beef, and the various vegetables.
Preheat a grill or grill pan over medium-high heat and lightly oil the grates.
Grill the skewers for 10-12 minutes, turning occasionally, until the chicken is cooked through and the beef reaches your desired level of doneness.
Remove from heat and let the skewers rest for 3 minutes before serving to allow the juices to redistribute.