rectangular plate/grate
Like these?
https://smile.amazon.com/Char-Broil-Cast-Iron-Smoker-Box/dp/B0001B50B2?sa-no-redirect=1
https://smile.amazon.com/Skyflame-Universal-Stainless-Charcoal-Rectangular/dp/B07MP4LRV8?sa-no-redirect=1