Blend all herbs, spices and olive oil until a pesto like paste has been formed.
Line bottom of slow cooker with sliced onions and half of lemon sliced.
Score lamb leg deeply on both sides. Rub Herb blend all over leg and place in slow cooker on top of lemon and onions slices. Place other half of lemon slices on top of lamb.
Cook on low for 8-10 hours depending on size of leg. I cooked a 2.3kg leg for 10hrs.
Strain juices from bottom of cooker for a delicious gravy!