Me too OP. I am on the lose weight but keep the other kinds of pounds mission!
For me decision fatigue is what derails healthy eating and any kind of change I want to make really. Having to constantly reinvent lunch or dinner but make it still tick all the boxes.
Here is what I am doing:
Breakfast 400cal: slow cooker porridge. Yep. Slow cooker. cooking while I am sleeping. No mess when I wake up either, since i cook it in a bain-marie in the slow cooker. I eat from the pot it cooks in. A little cocotte with a lid inside the slow cooker with a lid on and water up to halfway outside it. I pile it all in the cocotte the night before and a wifi switch turns it on at 4am and it cooks on low for three hours. Decision fatigue removed and I really want it when I walk in the kitchen because it is right there in front of me, looking delish and all it needs is a spoon.
40g oats, 120ml milk, splash of water, honey, and crucially - a cube of frozen double cream. (I freeze double cream in ice cube trays). if I don't add the cream then I am hungry again ten mins later. If I do, then i'm good until lunch.
Lunch 450-500cal: I work from home most days. and like I said I hate having to decide all the time on stuff. I have a baked potato every lunch, cooked in another slow cooker that comes on automatically at 7am, on high for 5 hours. I simply wrap a potato in foil and chuck it in the night before. This makes lunch dead easy because again - it is ready and waiting, already cooked. I do use butter, 15g, and toppings are tuna or beans or 70g cheese .
Weekend lunches are scrambled eggs on toast, or garlicky mushrooms on toast (with one portion of cream cheese stirred in)
Office-day lunches are cous-cous/pasta based.
Dinner again 500cal ish: this is the most variable as you'd expect. It's also where I get most of my veg. This tends to be something lentil/veggie based. If I got hold of some meat on offer. Mushroom and spinach lentil stew, pasta with frozen Mediterranean veg and pesto, Bubble&Squeak and 1/2 tin beans, kedgeree (frozen fish) , veggie biryani...You only need to find your groove with 5 or 6 repeatable easy meals.
Evening thing to stop me Netflix and snacking 150cal: Ovaltine. Seriously. 200ml milk and three teaspons (you don't need five like the packet says, they just want you to buy more).
YOUR FREEZER IS YOUR FRIEND - I freeze nearly anything and everything. In individual portions too (if you're single and cooking for one). The base of most things is onion and garlic, much easier to just take one portion of pre chopped onion and garlic out the freezer and crack on. Same with single portions of mash, make a load and freeze them in portions. Anything to reduce cooking friction because I bloody hate cooking. You know what to do and what you need to do, just reduce the friction and make it easy.
Your freezer is great for your budget too though, nearly everything can be frozen.