Preheat broiler or grill.
Place a large pot of water over high heat to boil the orzo. Salt the boiling water and cook the pasta to al dente according to package directions. Drain the cooked pasta and reserve.
While the pasta is cooking, in a large mixing bowl whisk together 3 tablespoons EVOO with the oregano, onion powder, garlic powder, some salt and pepper. Toss the lamb cubes in the mixture to coat. Thread the lamb onto metal skewers (wooden skewers are ok, too, just soak them in water for 20 minutes prior to use). Broil or grill the lamb until seared and cooked to medium, about 2-3 minutes per side.
While the lamb is cooking, prepare the orzo: Place a large skillet over medium-high heat with 2 turns of the pan of EVOO, about 2 tablespoons. Add the onion and garlic to the pan and saut until tender, about 5 minutes.
While the veggies are cooking, add the vegetable stock and about 2 cups of spinach to the bowl of a food processor and process until smooth. Add the puree to the pan with the onion and garlic to heat through, about 30 seconds. Remove pan from heat and stir in the reserved orzo, remaining whole leaves of spinach, feta, some salt and pepper.