Have this building (2-storey building with only 1 entrace - white double doors; 5 rooms / level, flat roof accessible with stairs inside, common on military bases, also found one in the southern part of Sitnik agroculture area) and build the stone oven inside it. Light the fire, then have the cooking pot in hand and try to attach it. The command will not appear. Inside the fireplace vicinity menu, it is also impossible to put the pot into the intended slot.

I tried it with empty pot, and also with pot filled with water. The building is the 2-storey one with one entrace, 5 little rooms / level, and the flat roof is accesible with a single door at the top of the stairs. I tried this on the first and second floor too. Worked in different type of buildings.