Here is a natural oven cleaner "recipe" you could use:

Sprinkle baking soda all over the bottom until it is covered completely with about 1/4 of an inch of baking soda. Then, using a clean spray bottle, I spray the baking soda with water until the baking soda is thoroughly damp but not flooded. After that, this lazy cleaner goes off and does other things. When I think of it, I dampen the baking soda again if it is drying out. Before I go to bed, I do that again. When I wake up in the morning, the baking soda can effortlessly be scooped out of the oven with a sponge, bringing all the grime with it. That's it! The only downside is that you need to rinse out the white residue left by the baking soda, but it sure beats cleaners with fumes!