Honestly , one child and all day , no I really don't understand how hard it is to prep a simple meal in advance.
Many people employ nannies, au pairs and childminders to care for multiple children and they all seem to manage yet one mother , one child and it's impossible. I think it's a case of not wanting to make it work.
I found maternity leave pretty limiting because it was boring but it wasn't exhausting, not with one child. My son's father worked long and unpredictable hours so could be home any time from 7pm til midnight so any help during the week was a non starter. We ate a lot of slow cooker meals, casseroles, chilli, anything that didn't need fussing over.
In the OPs situation how much nicer to have the main dish done so she can leave her DH to do the putting to bed whilst she dishes up and they sit down together the two of them by 7.30 and have time together for the evening. No to stomping off with a slice of toast and a bad atmosphere, she gets to hand over and he gets one to one time and they get time together. I'd have loved to sit down to dinner with my husband reliably before 8pm and its so easy to achieve.
Now the kids are grown my present partner and I both work full time, and we both work opposing hours at times so whoever has the time cooks or preps the meal. It isn't his job or mine it's whoever is physically present to do it so we can both eat at a decent time and spend time together. It's certainly not gender based. I had to work (from home) Christmas morning. He was more than capable of doing the prep but I got up early to do it, he then did the lion's share and we ate when I'd finished. You do what works best for all , if that means sealing some meat and veg and tipping them into a pot to cook and remembering to add jacket spuds at 6.30 leaving one person to simply make up a salad , cook a few green beans etc and dish up allowing for a relaxed meal and time to relax after ......why does it matter if the person doing it is male or female. Working out the best time efficient ways and getting into the habit of batch cooking will pay huge dividends when Mat leave is over too.