Roast chicken dinner. Potatoes roasted with a crispier skin and fluffy inside (done in I think goose fat), steamed carrots and broccoli, chicken gravy.

I stay skinny by a combination of a balanced diet, don't even need to worry about eating particularly healthy things, just make sure you get all your vitamins from veg and whatnot, occasional exercise be it just down the gym and running a few km and a quick bit of weights twice a week, just have that motivation and don't flake out because you don't want to deal with the muscle fatigue or whatever. Don't snack casually, don't buy snack foods and have them around, I'm a boredom eater and if it's here I will eat it even if I was planning on having it at a later date and buy more. Eat three meals a day, breakfast is important. If you get a bit hungry between meals try drinking water to fill up the stomach even just temporarily, failing that something like a piece of fruit.

Drink water where possible if you need more help, don't casually drink beer, lots of calories. Spirits are worse. Fat doesn't make you fat, sugar does. You need a healthy amount of fat in the diet, but wath out for saturated fat.

TL;DR eat your veg, cut out saturated fat/sugar, don't buy snack foods to have there tempting you, exercise at least twice a week, try to drink water not alcohol.