Fireplace knowledge ?

Hi there I am hoping someone will be able to advise on this fireplace. As you can see from the pics that I have a small fireplace that only just allows the wood burner to fit and I would like it bigger. I am wondering if there is likely to be a builders opening ?
The walls in this house are solid and at least 9" thick. There is a mantle that runs the width of the wall and into the recess that protudes about 4 " from the main wall/breast . There is currently a steel lintel that appears to be supporting the main breast.
It's a bit of an odd set up to me as there is no obvious breast it is the whole wall minus the recess.