I was in the exact same situation as you about 3 years ago.
I used to try and prep dinner while DS2 napped and before DC1 came in from school.
I’d try to make things that we could all eat but the kids could have earlier than us.
Things that worked were:
Cottage or Shepherds pie. Use frozen mash as someone else suggested. You will not know the difference. Make the mince and veg part during nap time, put in a dish. Make mash in micro, fork it over the top with some cheese and out in oven half hour before needed. Sometimes i’d just do this part straight away and cover with foil to keep warm and lightly heat a portion in micro.
Spag Bol. Make the sauce at nap time, even cook the spagetti and drain into cold water to keep.
Fish Pie - same as cottage pie above
Mac n cheese as you have already done.
Baked potatoes - wrap each one in foil, put in slow cooker for 6 hours on low. Ta da! Instant dinner with choice of topping like beans, cheese, tuna, salad etc
Some nights it’s fine to just nuggets and chips for the kids and someone nicer for the grown ups!
Even now, despite both mine being in school, i still tend to prep dinner in the afternoons. I do have the luxury of not working afternoons tho which makes this work for me.
Trying to see to tired hungry kids whilst making dinner is THE WORST!
Sacrifice some time during nap time and do it ahead.