Okay, this sounds stupid, but it's really good, I make it all the time, it's unbelievably cheap, and a bag of potatoes lasts a good week.
You need:
3 Potatoes
1 Tin of carrots
a few sprouts or some green veg that can be mashed.
Tomatoe sauce
Boil the potatoes
Meanwhile boil the sprouts and add a bit olf salt and cook up your carrots.
When everything is ready, mash the potatoes untill very fine, put it all on a big plate, and mash it toghether
Now the wierd bit, add tomatoe sauce. mash it toghether again, if you want you could add in steak pieces or chicken pieces for protein...
Put on a plate and eat.
It sounds stupid, but I love it

really
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another:
You'll need
Homemade soup
Potatoes
Take al ook at John's homemade soup recipe, and make a pot of it, boil potatoes and mash, and mix the potatoes with the soup on a plate, and eat. Another great meal with plenty of veg, and protein weither you added any meat or not.
I'll add some more if I can think of any
(I really do just think of meals at the top of my head in the middle of cooking

)