Toast the spices. Place 2 tsp coriander seeds and 1 tsp cumin seeds in a small dry skillet, then set over medium heat. Cook, shaking the pan often, until the spices are fragrant, about 2 minutes. Transfer to a mortar, then finely grind with a pestle. Set aside.
Make cilantro and onion mixture. Place 1 cup loosely packed cilantro in the bowl of a food processor, then add ¼ red onion thinly sliced and 2 cloves of garlic. Pulse until finely chopped (but not a paste).
Mix the ground lamb. Place 1 lb ground lamb in a large mixing bowl. Add the cilantro-red onion mixture, the ground spices, ⅓ cup feta cheese, 2 tsp garam masala, 1 tsp Kosher salt, and ¼ tsp black pepper. Use your hands to thoroughly mix, about 2-3 minutes. Cover with plastic wrap, then refrigerate for 30 minutes.
Soak the skewers. If using wooden skewers, soak in water while the lamb is chilling, for at least 30 minutes. Drain and pat dry.
Assemble the kebabs. Divide the mixture into 8 equal portions, then roll into round balls. Press a skewer into each portion of meat, then use your hands to press the mixture into a 3-inch oblong shape around the end of the skewer. Repeat until all kebabs are prepped.
Grill the kebabs. Heat a grill over medium-high heat until it reaches about 400-425°F (205-220°C). Coat with grill spray, then carefully add the kebabs to the grill. Cook for about 6 minutes, turning the skewers every 2 minutes until they are browned on all sides and fully cooked. The lamb should register around 155-160°F.
Garnish, then serve! Transfer to a large platter then serve with lime wedges, fresh mint, and thinly sliced red onion. I like to serve Greek yogurt garlic sauce on the side. Enjoy!