Many years ago I fitted a gas hob in our kitchen worktop. It was above base units and when not in use it's cover was almost flush with the worktop surface. I have since moved from that premises.
To use the hob one had to raise the hinged cover back to the wall. The cover then formed a splashback and also raised up the hob to above the work surface level.
For fitting, the whole unit was effectively in a flanged metal box with a
hinged cover. The box could be dropped into a cut-out in the work surface, be connected to the gas supply. (I forget if it was rigid or the bayonet rubber type of connection) It had clips under the box which fixed it to the underside of the work surface to form a fixed unit.
I cannot find anything like this now and wonder if it is no longer considered gas safe. It was ideal as it could form part of the work surface when not in use and I would like to install one again.