Back to basics. Small portions of food that kept be left half eaten and finished later. I don't know your health situation but if you can, eat high fat, high sugar foods to keep you going and lift your mood. Eat when you feel like it, not because the clock tells you it is a meal time.
Some suggestions
Breakfast cereal with full fat milk and sugar if preferred - any time of day. It can help you sleep if you eat it before bed
Jam sandwich
A 'picky plate' - cooked meats, cheeses, fruit, nuts, crackers or biscuits, bit of cold pie, hard boiled egg
Soup
Cheese on toast
Beans on toast
Supermarket single serving hot pudding (sponge pudding with syrup, there are other options) that ding in the microwave
If you like strong flavours, those little pots of fish or meat paste can make a tasty small sandwich. They will keep in the fridge if you can't eat a whole pot at once.
If you really can't eat, Complan is a good source of nutrition and the drinks are pleasantly flavoured.
You need to be aware that constipation may become a problem if you don't eat enough so try and get some fibre in to your diet.