Something I really enjoy and found very helpfull is tuna salad.
Get tonnes of lettice or baby spinach leaves,
Chop us some carrats, sweetcorn, and tonnes of other stuff u want, stick it in a giant tub and it'll last all week. then every morning take a large hand full, drizzle with a flavoured olive oil (sun dried tomato is great) salt pepper and crack open a tin of tuna (in water is much better for you, not oil)
its really easy and takes 10mins once a week. And if thats not enough for you have a lil jacket potato with it. Just try not to add loads of butter and cheese.
When ur bored with the tuna, try cutting up BBQ chicken, or cook a steak and cut in to lil strips.
there are loads of things that are easy, just as cheep and much better for you than even the best subs.