Its all very daunting where to begin?
Keep it simple, plan one or two meals ahead of what you may have if you are looking to do something different for each meal.
Another way is to make slightly larger portions of lunch so that it can be for dinner too or lunch the next day, so you have less to worry about later on.
If you want to be a little but more savvy, using the like of a slow cooker where you can batch cook 4-6 meals and that could be a weeks worth of dinners done on the weekend with minimum effort in the cooking process, plus only one clean up too required.
One of my own methods is to have a set mixtures of food that i know well will meet my daily goals and I rotate through those, for instance I have 4 different go to breakfast options, below you can see a smaple of these.