I have two good meals on my 500 cal days. I can make a substantial cottage pie using turkey breast mince, or a fish pie, for around 250 cals, I make 4 and freeze 3. For lunches I find mushrooms very useful at 2 cals each, I have loads, fried in spray oil, on 2 slices of toasted 50/50 crusts away bread (45 cal per slice), with marmite. Scrambled egg whites are good too at 20 cals each.
When I want to save time and have the counting done for me I buy M&S roast lamb meal for one, 170 cals, or their Count on Us filled Yorkshire puds at 210 cals.
Home made soups are easy at around 50 cals per serving, and so much more filling than cup-a-soups, which have about 90 cals.
I used to be a walking Weight Watchers point list, but now I am learning calorie values instead. Good luck to all who are embarking on this regime, I hope you will find it as easy as I have (I do alternate days).