What are we doing for dinner?

I know I seem to be dwelling on food but indulge me.
So, I try to work in our home office largely because I am an hour and a half (by car) from my actual office. My beloved partner, who is only 20 minutes by city bus from his office, tends to work there at least part of the day. This is good as our home office is too small for us both to be working comfortably. However, for some reason my dear, dear partner seems to think that, since I am at home, I should also be thinking about dinner. Thus, each evening when he is on the bus he calls and invariably asks the question, "What are we doing for dinner?"
Now, I admit, some evenings I procrastinate by locating interesting recipes on epicurious.com and preparing them. Usually, however, I am just as uninterested in thinking about what we're doing for dinner as he is. Frequently I am annoyed by the question because it seems to place the onus on my shoulders (we could give him the benefit of the doubt and say it is ONLY because I am the one at home and has nothing to do with gender but I know this is just incorrect). I've tried various approaches to voicing my annoyance with the question. "I haven't thought about it." "I don't care." "What you eat for dinner is your own business." "I'm sure that you'll put together a very nice meal once you get home." "Can you stop asking me that? It's not my responsibility to prepare dinner!" Unfortunately, I seem unable to eliminate both the question and underlying assumption that I should prepare dinner.
It's infinitely frustrating.