I love cooking, and having someone take the baby so I can cook in peace was my idea of heaven when she was that age, so I'm the wrong person to ask, but if it's a massive chore for you, then I think it's reasonable to ask, sure.
My feeling is that when he's at work, you're at work in the house. When you're both home, you share home duties. He doesn't work long hours, frankly, and being at home with a 5 month old is pretty brutal.
Now that mine is 18 months, I do get annoyed when I come home after an 11 hour day and my husband (who's been at home all day with her) hasn't even started dinner, so I'm scrambling to get something on the table by 7pm so she can be in bed by 7.30. But that's a different matter altogether. One meal a week from a man who's only out of the house for 9 hours is hardly an awful thing to ask.
As for this:
Also, women have to keep housework in perspective in terms of all the other things that are required to keep a house going. For example, my husband doesn't cook often but he always makes sure our computers are working, that our gutters are free of leaves and that our sink is draining properly. OP, would you be prepared to change the lightbulbs or unblock the drains once in a while (and more importantly, do you)?
How often do your computers need fixing and your gutters clearing? Because our computers need a bit of a tweak once every six months, our gutters get cleaned after a storm or about every 3 months, and a lightbulb takes 30 seconds to change and hardly requires A Man to do it, FFS. And all of those jobs can be put off till it's convenient to do it (within reason).
Housework, by contrast, is every day, and it's unrelenting. If it doesn't get done every day there's no clean clothes, no clean dishes, no food on the table. My three person household requires 3 hours a day of housework to keep under control, and the occasional all-day deep clean. I have that well in perspective compared to changing a lightbulb. Jesus.