With sharp knife, slice about 1" off top of each artichoke; cut off stem near base. With scissors, trim about 1/2" off top of each leaf. With sharp knife, halve each artichoke vertically; then scoop out and discard the fuzzy center or choke.
Place artichoke halves in slow cooker; add hot water and lemon slices. Cover and cook on HIGH 4 to 5 hrs or until done. Drain; serve with sauce.