what's the best way to clean a really dirty oven without harsh chemicals?

The most effective, gentle way to clean a heavily soiled oven is to use a paste made of baking soda and water. It is safe, inexpensive, and highly effective at breaking down grease and burnt-on food.

Here is the step-by-step process:

1. Prep: Remove the oven racks, thermometer, and any loose debris or large bits of burnt food.
2. Make the paste: Mix about 1/2 cup of baking soda with 3 tablespoons of water. You are looking for a spreadable consistency, similar to a thick cake frosting. Adjust the ratios if needed.
3. Apply: Wear gloves and spread the paste all over the interior surfaces of the oven (avoid the heating elements). Focus extra paste on the areas with the most buildup. The paste will turn brown as it picks up the grease.
4. Wait: Let the paste sit for at least 12 hours (or overnight). This gives the baking soda time to break down the grime.
5. Clean the racks: While the oven sits, soak your racks in hot, soapy water in a bathtub or large sink. Scrub them clean once the soak is complete.
6. Wipe out: After the wait time, use a damp cloth or a silicone spatula to scoop out as much of the dried baking soda paste as possible.
7. The Vinegar Final Step: Put a little white vinegar in a spray bottle and lightly spritz the remaining baking soda residue. It will foam up, which helps lift any remaining stubborn bits. Wipe everything clean with a damp cloth until the surface is clear.

If your oven glass is particularly dirty, you can use a damp microfiber cloth dipped in a little extra baking soda to scrub it gently without scratching the surface.