I put them in the oven with a oven safe bowl filled with water and lemon juice, and put the oven on at 200 degrees for a hour and steam them, then take them out when they are warm and wipe all the gunk off.
Works for oven racks too, and also cleaning the WHOLE oven, and leaving it smelling all fresh and lemony

Oooo that sounds awesome! I'll have to dry that!