It took me ages to get the balance right - in the week I leave my house at 6.30am and get home at around 5, exhausted. I tend to spend a couple hrs on a Sunday afternoon prepping food - I make a big batch of stew/soup in the slow cooker and freeze five portions, then also prep veg by peeling and chopping cucumber, potatoes and carrots - all stored in water in the fridge.
Most of my fridge is full of foods that are already semi prepped/at least chopped and put in a jar. It means when I get home I can just throw ready cut handfuls of veg into a pan with some noodles / on the side of some air fried meat.
I also make breakfast (porridge with fruit) in the microwave at work - once a week I pop out on my break to the shop near my school and buy bananas and milk. It's all about optimising what time you have and using some of your free time to ensure the healthy options are almost as convenient as the unhealthy :)