Yes, Lynne is serving dinner wearing just an apron. Nothing underneath at all. She could have been feeling kinky and decided to strut around nude; she could have drawn a bath and then realised it was her time to cook; she could be preparing a quick dinner for George before they go to the the theatre and didn't want to put on her best dress to cook in or some old clothes that she'd just have to take off again. She certainly didn't want to get any hot oil on her bare flesh as that would be painful, so she's sensibly put on an apron.
Lynne's cooking isn't always this bad. If it was then George would not be so happy to have seen Lynne bringing him his dinner. He is glad that dinner is served, although this may just be due to the amount of time he has waited for it, because he expects it to be tasty. Alternatively Lynne never cooks and has decided to have a stab at it tonight. George is hopeful but it has taken far longer than he expected it would. It seems light outside so it can't be too late. Maybe he is one of these people who calls lunch dinner.
I wonder what Lynne has cooked that a) is so disgusting George will not even taste it and b) becomes in edible when it is cold. Granted, most hot food loses its appeal when it drops in temperature but does any actually become inedible? Perhaps it is something similar to liver and onions where the well cooked meat becomes even tougher when it get colder. Lynne knows that she's cooked it a little too much but knows that if George eats it quickly then it will still be edible. That's a risky meal to try for a first attempt. She should have chosen a classic meal to cut her teeth on, maybe adding a twist of her own, and then attempting something a bit more adventurous if this dish was received well.
George hates it and looks as though he will throw it out of the window, or at least put it on the windowsill where it will cool down quicker. He cleverly thinks his last thought rather than saying it out loud as he knows this has got both him and Lynne in trouble in the past. As much as he dislikes Lynne's cooking, he doesn't want to hurt her feelings.