I think i just completely ruined the ratatouille that my housemate had spent ages preparing for her sister who's just been burgled.

I went downstairs after my evening nap, switched the oven on to heat up, then went into the lounge to watch tv. When i returned to put my pizza in the oven, i found there was a big dish of delicious-looking ratatouille in there already. Assuming my housemate had just put this in to cook, i put my pizza on the shelf above. When it was done, I was careful to make sure that I left the oven on so that I didn’t disrupt my housemate’s cooking. Half an hour later it suddenly occurred to me that perhaps the ratatouille had been cooked earlier and left in the switched-off oven to cool. It's now black. Housemate hasn't noticed yet. What do i do? :(:(:(