Next time put your pie pan on a cookie sheet so if it spills its just on the pan not in your oven - learned this trick after spilling pumpkin pie in my oven!

Thanks, PPs (OP here). I will try both methods. I bought the plastic scraper tonight and tried a small spot and it works for scraping it off. I think I'll scrape what I can first and then spray water and wipe off the rest. Not tonight though; too tired. But I won't wait a month like the rotten egg salad on the counter poster.

At the hardware store, on the kitchen implement aisle, I got a flat plastic scraper that I use for my cast iron skillet. Cost about 19 cents. That might help on scraping the bottom of an oven.
If they don't have it in the kitchen section, I think in the paint section you can buy a plastic putty knife (wide, like you'd use for applying spackle to drywall.

I'm sympathetic to wanting to avoid the chemical cleaners, but in some situations they're the only thing that really make it easy.

Not a fun job--sorry that happened, OP! Because I wouldn't want to use any kind of chemical, I'd carefully spray water (I have a spray bottle just for water) or use soaking wet paper towels to saturate/soften the quiche remains. You might have to use a lot of paper towels, but eventually it'll all soften and wipe up. Good luck!

Please excuse my naivete for not knowing the best way to clean this. I made a quiche last night, but when I was putting it into the 400 degree oven, it sloshed over out of the pie plate and splattered all over the inside of the oven door and the bottom of the stove. Made a huge mess and now it's baked on... yuck. I don't cook much and this is by far the biggest mess I've ever made in there. I have an old school gas stove, and while it's bad ass, I'm not sure the best way to clean it. Don't want to use one of those gross chemical spray cleaners.

TIA for your advice! BTW the quiche turned out great.