What I generally end up doing is spraying some commercial, chemical based oven spray in my oven and then cleaning it and getting a chemical-spray induced headache. Lovely.
But there is a chemical free way!
The night before you want to clean, get a bowl and fill it 1/2 c. of ammonia. Close the door and let it sit all night (okay, this is a chemical but it's the pre-wash part so it doesn't count).
The next morning remove the ammonia and let the oven air out for a few minutes.
Now, take 5 teaspoons of baking soda, 2-3 drops of liquid dishwashing soap, and white vinegar and make a paste (you thought I was going to say lemons didn't you?). Scrub the inside of your oven with the paste and a cotton cloth. Get a spray bottle and spray with water to rinse then wipe dry.
If your oven is UBER nasty and you have some seriously tough stains, mix 1 c. baking soda, 1 cup of salt and enough white vinegar to make a heavy paste. Rub all over your oven. Turn oven on to 500 and leave for 30-60 minutes. Turn off. Leave the door closed and allow to cool. Spray with a water bottle to rinse and wipe dry.
The good news is that this is mostly chemical free. The bad news is that it still can be smelly (just not burnt-oven/chemical smelly).
If you think you hate cleaning your oven more than I hate cleaning mine, plead your case in the comments! Wouldn't an "I hate oven cleaning" haiku be fun?