How long is your trip?
I would simply leave Magic Kingdom, go to Capt Cooks at Poly and have lunch there. Otherwise I would do Casey's Corner inside of MK.
MK is by far the worst park to get food in IMO.
You could walk all the way to Poly, have lunch, and walk all the way back before you get done with a sit down meal likely. Just waiting to be seated could take a little while you never know. Flip side going to some place like Casey's or Cooks you can mobile order but with Casey's you might need to take your food elsewhere if there is no seating.
You can do a sit down dinner somewhere after the park closes to day guests.