1. Heat a grill or grill pan. Place ground coriander and anise seeds in a medium bowl. Add garlic, paprika, cayenne pepper, and 1/4 cup olive oil. Season marinade with salt, and stir until combined. Add sirloin cubes, and stir to coat.

2. In a medium bowl, combine mushrooms, onions, and remaining 1/4 cup olive oil. Season with salt and pepper; toss to coat.

3. Divide steak among 4 skewers; thread, leaving 1/2 inch between each cube. Divide vegetables among another 4 skewers; thread.

4. Grill the sirloin kebabs until well browned and medium rare, and grill the vegetable kebabs until glistening, tender, and slightly charred, 5 to 7 minutes for both. Serve on the skewers.