Keeping baked-on messes in check will reduce the amount of fumes released every time you turn on your oven. But noxious, chemical oven cleaners can be the harshest products in your kitchen because they contain corrosive ingredients that can burn skin and trigger asthma attacks (particularly if they're in aerosol form). I’d also skip the stove's automatic-cleaning feature, as it uses up fossil fuel and releases all that crud into the air, but if you do use it, be sure to run your exhaust fan the entire time.
It’s best to clean spills and splatters as soon as possible after they happen. For fresh spills, spray or sponge on your nontoxic cleaner (keep it off electric elements), or a solution of 2 cups of hot water, 1 tablespoon of natural dish liquid and 1 teaspoon of borax. Let it sit for 20 minutes, scrub the crud off, and wipe dry with a clean cloth. For really greasy messes, wipe out as much as possible with crumpled newspaper first, then spray the solution and let it sit for 20 minutes before wiping it away.
Related: 9 Easy-to-Make Non-Toxic DIY Home Cleaners
For older spills, you need to invest some time to reduce the amount of elbow grease required. Moist baking soda is nontoxic and surprisingly effective at loosening even really old baked-on gunk. The trick is getting it to stick to vertical surfaces, and keeping it moist (baking soda does very little if it's dry). After some experimenting, here’s my answer: Mix 2 tablespoons of cornstarch with 2 cups of cold water in a saucepan. Bring it to a boil, whisking constantly, and simmer, still whisking, until it turns clear and gooey. Mix in about a cup of baking soda, or enough so that the mixture becomes a paste with the consistency of yogurt. Smear the paste in a thin layer over all the walls of your oven, keeping it off electrical elements as much as possible. The layer should be thick enough to be white, but doesn’t need to be any thicker than that. Once an hour for the next 12 to 24 hours, at least while you're awake and at home, spray the baking soda paste with water to keep it damp. You'll see the baking soda start to turn brown in spots as it works. After the 12- to 24-hour period, scrub the paste off a test area to see if the grime is well loosened. If it is, get to work on the rest of the oven. Scrub stubborn spots with steel wool or a steel coil scrubber (your fingers will thank you if you use your sponge to hold it). When you're finished, rinse with water.