In addition to mental illness, I have a few fatiguing illnesses along with chronic pain. I have learned to make meals very easy, especially nights I am wiped out. Just a few ideas: sandwiches, hot dogs and beans, Lean Cuisine meals, etc. Look around in the frozen food section for some easy ideas.
When I am struggling, I will also use a crockpot, starting dinner in the AM, letting the crockpot cook all day long. I also will sometimes cook a full meal in the morning, before I tire out, and will re-heat it at dinner time; this way I can cook and clean up in the morning.
If I am very ill and can not attend to dinner, DH will help out. (He works, too.)
Just a couple of ideas to help out when you are exhausted by dinner time.

WC