If the door is Aluminum - try this on for a simple idea:
Get one or two button-size magnets - look for rare-earth or alnico types. (If you have / find some fridge magnets that are strong enough, you can "scavenge" them.) They should stick to the steel mid-section through the aluminum door.
First, dry-test it with one in the center - and see if it holds tightly enough. If not, try two - one in each top corner. Two might provide a tighter seal, if you want that.
Once you find a scheme that works, clean and lightly sand the spots where you want the magnets, then stick them in place and cover them with 100% silicone caulk, and let it dry before cooking with it. Once it dries, the silicone should be able to take the heat. An alternate would be to create some small aluminum "pockets" that will hold the magnets and silicone or weld them in place (if you know someone who can TIG-weld aluminum)
If you do this, you will probably also need to add some type of simple, fixed handle - in order to allow you to grip it without burning your fingers.