Garage Door in fill

Most inspectors now allow you to build straight off it , after all it's made to take the weight of a vehicle going over it , on the rare occasion you may get a jobs worth who may want you to tooth out the bricks either side where the pillars are and put a catnic lintel across and build up off that , but it's rare , and to be honest the only weight bearing down will be the new bricks , as the window is held in place on the sides and fixed to the existing pillars , hope this helps

I normally do single skin of brickwork on slab and timber stud with kingspan for internal thanks Allan

It’s not the thickness of the slab that’s the issue, it’s certainly strong enough to take the weight of a small wall and the window, it’s the transference of moisture from where the slab goes straight to the outside where when it rains for example, the moisture will pass through to the inside and create a damp floor. You will probably have to create a damp proof membrane to separate the slab from the outside wall which will entail having to cut through and remove the outer section of slab therefore creating the need for a new foundation. Garage floors are normally lower than the internal house floor so we normally build them up with a timber suspended floor with insulation between the joists or a damp proof membrane over the slab with a rigid insulation and floating chipboard floor on top.

It's good apart from you would not use a catnic lintel below ground it should be concrete lintels other than that it's a good answer