In a large glass measuring cup, whisk together all the ingredients for the marinade.

Place the steak into a zip-top bag and pour half the marinade over. Seal tightly. In a separate bag, repeat with the chicken and remaining marinade. Chill in the refrigerator at least 3 hours or up to 8 hours.

In a medium bowl, combine about half the onions, peppers, and tomatoes with 2 tablespoons of olive oil, and salt and pepper to taste.

In a separate bowl, combine the other half of the onions and mushrooms, and season with salt, pepper, and 1 tablespoon of olive oil.

Assemble the steak, layering with the mushrooms and onions. On separate skewers, layer the chicken with the peppers, onions, and tomatoes.

Preheat the grill to medium-high heat, about 425° F. Brush the grill grates lightly with olive oil.

Place the skewers on the grill, cooking the steak, rotating occasionally, until it registers 140° F, about 7-8 minutes. Cook the chicken until it registers 165°, about 10-12 minutes, again rotating occasionally.

Use tongs to remove the kebabs from the grill and let rest for 5 minutes before serving.