The walls and ceiling here are covered in metal plates, with intricate carvings and reliefs depicting terrible rites by some lunatic cult. At the GM's discretion, there might be clues in the reliefs, or there might be bodies here, burned into a charcoal state.
Either way, upon triggering, the exits seal up, and the plates begin to grow warm. Within 3d4 minutes, they will go from being warm, to hot, to red hot. At this point, characters caught in here begin to take 1d4 HP per minute from heat damage.
The area is likely too big for a Dispel Magic, but should one be available that can cover the entire trapped space, it might or might not disable the trap (GM's decision). Magical cold spells, such as Cone of Cold, directed upon a section of the plates, might cause them to fail. If so, the entire trap might fail (again, GM's decision). Thieves can use their skills to disarm this magical trap, with the usual penalties or bonuses.
The oven will continue to operate for one full day, after which it cools down, and resets.