How can I get nutrition assistance for my struggling, mentally challenged, and widowed uncle (70+) who lives alone?

Go to Virginia Division of the Aging:
http://www.vda.virginia.gov/aaalist.asp
and click on your locality.

SNAP is an assistance program as well, but for someone who could probably benefit the most from prepared meals, Meals on Wheels would be very helpful.

In our area, MOW are delivered M - Fri, but recipients can ask for weekend meals. Daily cost is $3 and I believe $5 for each of the weekend meals.

Another option, if you have HIPAA authority, is to contact his primary care or general practitioner physician and ask if he can script for an aide who could help him generally but also with putting meals in the microwave.

Or perhaps you could do that for him as well, depending on your availability and proximity to your uncle.

Supplemental liquid nutrition such as Ensure, Boost, etc. might also be an option. We bought Dad's out of pocket; I'm not aware ift any insurance coverage or agency would pay for it (unless it was for someone with a stomach tube), but you might contact the manufacturers and see if they have discount programs for needy seniors. Some pharmaceuticals do that for patients who can't afford the full amount of their meds.

Search your states website for elder affairs.. See if meals on wheels are available or what other services are available for him.