You could squeeze between two flat heated plates, To allow steam to vents, a number of small holes would do it. With uneven objects a high temp radiant source would work and the grid could be sparse - like chicken wire
I was thinking waffle iron / sandwich press, both of which seem to work fine without much in the way of venting (though if you tried to cook broccoli in a waffle iron that might become more of an issue?)
I think microwaves work fine for boilable food(Broccoli, rice potatoes etc) and a pressure cooker would also work. A pressure fryer (heats above Maillard thermal transition) fries very well at KFC's and Popeye's etc all over and can have both thermal input as well as microwave input (heats food all the way through fasts - versus thermal gradient = fried food in 3 minutes)
These should all work in space in constrained spaces.
That's an interesting idea, I would expect microwaves to be practical in zero-g, but a pressure cooker might be trickier, my naive intuition is that the contents wouldn't stay on the bottom of the pot to be heated, and would also float into the valve?
