In a large bowl, combine the ground beef, ground lamb, grated yellow onion, minced garlic, chopped parsley, cumin, coriander, salt, and black pepper. Mix gently with your hands until just combined.
Divide the meat mixture into equal portions. Mold each portion into an elongated oval shape around flat metal skewers or soaked wooden skewers.
Preheat the grill to medium-high heat. Lightly brush the grill grates and the formed kofta kebabs with a small amount of olive oil.
Place the skewers on the grill and cook for 6 to 8 minutes, turning occasionally, until the meat is browned on all sides and reaches an internal temperature of 160°F.
While the kebabs grill, prepare the Greek salad by tossing the diced cucumber, cherry tomatoes, sliced red onion, and crumbled feta cheese in a serving bowl with the olive oil and fresh lemon juice.
Remove the kebabs from the grill and serve immediately alongside the fresh Greek salad.