Can't go wrong with a dog & fries at Casey's Corner. There's a few seats inside, but mostly outdoor seating under umbrellas, and the castle view ain't bad!
If I may also suggest what my Wife, Son and I usually do at least once for lunch at a quiet "little-known secret" place to eat and relax:
They love the tuna fish sandwich at Columbia Harbor House, next to Haunted Mansion, whereas I prefer a Casey's dog. We split, and I'll get a dog and fries (although I think they're the same at both places).
My Wife & Son order their stuff, along with a drink for me at Columbia, that way I'm not leaving a trail of soda and wearing most of it, too.
Here's the "secret hidden gem": Rather than sit downstairs, head upstairs, and for an added bonus, there's seating on the "bridge", whereas you can look down at the guests as they go from Fantasy Land to Liberty Square. Last August, it was quite busy overall at the MK, but nice and peaceful for recharging up there.
There's a station with condiments and restrooms upstairs, too.
Just a little friendly advice...Happy Planning