This Minecraft Barbecue Design utilizes the Barrier Block and the Invisible Item Frame.
See this Minecraft BBQ being made in the video below:
Commands used in the video:
/give @s barrier
/give @s minecraft:item_frame{EntityTag:{Invisible:1}}
Below is a similar design, just using Iron Trapdoors on Black Concrete Blocks instead of Loom Blocks. Also features Gray Carpet placed into Invisible Item Frames on the front for doors.
Below is a popular variation that does not use Barrier Blocks or Invisible Items Frames:
Simply place some Items Frames onto Irons Bars for the side shelf, and Iron Trapdoors inside the Item Frames on the Front.
