Flasks for soup or food flasks for things like stew. You can cook a stew overnight in a slow cooker and then put it in a food flask for work.
Hugh F-W does a sort of home made pot noodle, prep the day before then just add boiling water.
Have a stash of fruit and other snacks on your desk.
I have a 'bento' lunch box with different compartments so I can do:
1-carb - noodles, rice, cous cous, bread, maybe a few crisps
1-protein - cheese, hard boiled eggs, chicken
1- veg - salad (with a nice dressing in a screw top jar) green beans, steamed asparagus, carrot sticks, cucumber sticks, corn on the cob (cooked obviously) pepper strips
1-fruit - a satsuma, slices of melon, grapes, cherry tomatoes
1-treat - dried fruit/nuts/ chocolate if I'm having veg sticks I might make this a dip or hummus
It means I don't need to think too much or do a lot of prep.
Obviously you can change the fruit to veg or leave out the carbs altogether but the compartments make it easy to have a variety of foods.