I found out after owning my oven for several years that it has a self-cleaning feature that works really well! If yours does not, I've used fume-free Easy-Off with excellent results. Here is a link to an article with DIY oven cleaners for a natural approach. I hope this helps!
My oven has a steam cleaning feature that is ok, but some baked on stains, especially the racks need more, so I have used the no fume Easy Off on a cold oven successfully.
I made a paste of baking soda and water and spread that all over the oven. Then you spray it with vinegar which activates the baking soda. I usually let it sit for a while then scrub. It will leave a white residue that I just wipe out with a vinegar soaked paper towel. If you have kids or pets this is a natural way to do it without all the fumes. It will take some scrubbing but I was very happy with how mine turned out.