When people feel useful, it's a "positive" distraction for them, and can be helpful for the caregiver. Some things the loved one w/ dementia can do while you're cooking:
1. Fold laundry at the kitchen table (even if you use clean dish towels that are already folded - dump them into a basket as if they were just laundered.)
2. Find a way to incorporate help in making a non-crucial part of the meal - ex: tearing lettuce for the salad.
3. Have the loved one sit at the kitchen table w/ a family photo album, which is more familiar and may be less distracting than TV or radio programs.
Hope this is helpful!