To make the dressing, combine all the ingredients in a food processor and blend until smooth. If the dressing is too thick, add more milk and blend further. Place the dressing in an airtight container and refrigerate it until you’re ready to use it.
Soak 12 wooden skewers in water for about 30 minutes. Preheat your grill to 450-500 degrees.
To make the kebabs, place the onion, garlic, and parsley in a food processor and blend until the ingredients are fine chunks and well blended. Add the beef, lamb, and all the spices and seasonings. Blend until you have a well combined, pasty meat mixture.
Divide the meat mixture into 12 equal portions. Form each one into a sausage shape about 1-inch wide and insert a skewer through its center.
Lightly oil your grill grate. Carefully place the kebabs perpendicular to the metal spokes of the grate. Working in batches, grill the kebabs for about 4 minutes until golden brown on the bottom, then flip them over and grill for another 4 minutes until the other side is also nicely grilled.
To assemble, toss the salad greens with the creamy feta dressing, remove the skewers from the kebabs, and place them on top of the salad.