The Old City has surprisingly good food hiding among the tourist-trap restaurants right by the palace walls.
Restaurants immediately outside the Grand Palace gates are almost universally overpriced and mediocre — designed for one-time tour-bus traffic, not repeat local custom.
Walk 5–10 minutes toward Tha Tian pier or into the Maharaj Road area — genuine Thai restaurants serving office workers and locals, much better value.
A modern development near the river with a curated food court — reliable, air-conditioned, good for a break from temple-hopping heat.
Look past the main tourist strip into the sois behind — som tum carts and noodle stalls serving 40–60 THB meals to Old City residents, not tourists.
Eating right before or after your temple visit rather than mid-tour avoids the worst of both the heat and the tourist-strip crowding around lunchtime.
If a restaurant has laminated photo menus in five languages directly facing the palace gates, it's built for one-time tourist traffic — walk a block further for something better.