It sounds like it’s not zoned as a secondary unit. Usually the enforcement in this situation is to remove the range (already done) and possibly make you remove any shower/tub. Friends were renting a house in north park and another friend was renting the converted garage… the previous tenants were law students who stopped paying rent and called in the violation just to be punks (per my friend). The $&&$ hit the fan while their friend was in the unpermitted conversion.
When we built our companion unit, turning our SFR into a multifamily, getting the gas meter was the very last thing done… happening only after occupancy had been given by the city of San Diego. That’s why you don’t have the meter.
Theoretically, you might be able to legally convert it to a multifamily if you meet the kafka-esque requirements (assuming you are city of San Diego)