Trim fat from meat. Cut to fit into 3.5-6Qt. slow cooker. Combine oregano, lemon peel, garlic, and salt in small bowl. Sprinkle evenly over lamb and rub lightly. Place lamb in crockpot. Sprinkle with lemon juice.
Cover and cook on low for 8-10 hours or on high 4-5 hours.
Remove lamb, discard fat, chop meat and set aside. Add spinach to cooker (with juices), stirring until spinach is wilted. Add cooked orzo, feta, and lamb; stir to mix.
A sprinkling of toasted pine nuts (pignoli) is a nice touch.