Most of us skip breakfast thus putting a small fast into each day but when it comes to lunchtime we are so hungry we eat all the wrong stuff. Lunch does not need to be complicated. Mine usually consists of a premixed salad, yoghurt and an orange. If I am still hungry I'll eat some baby carrots with ranch dressing. Notice none of these need to be cooked and I have all the food groups covered except perhaps for the grains. To get that around two I'll make myself a bowl of quaker oats, still no cooking just hot water. You will also notice that none of those things are really expensive. That's important when you are on a fixed income.
Here are some other ideas for quick, healthy lunches:
1) Greatist has a list of Healthy Meals in 12 minutes or less. It's all three meals but no one says you can't have Breakfast for Lunch. My favourite are the lettuce wraps, you can put anything on them and they are glutin free.
2) Cooking Light has a slideshow for 51 Healthy Lunch Recipes and Ideas with an Eastern Europe flavour. I haven't tried any but they are a few that I would like to try. The Tuna, Avocado, Pickled Onions Sandwich looks good. Cauliflower Po'boy sandwich looks interesting too.
3) 30 No Cook Lunch ideas from Cooking light has some tasty looking salads.
The one thing you will need to remember is that vegetables & grains should be on your shopping list before anything else. Even on a fixed income vegetable provide excellent nutrition and they go further than the packaged or frozen stuff which means don't let the initial cost scare you. Remember a $3 head of leaf lettuce can serve dozens of meals and it is as versatile as bread maybe even more so.