All OTR's are 15" deep by design. They will all stick out from your cabinets as they do from every other single kitchen that has an OTR. A 12" deep OTR would be pretty useless at providing enough coverage to capture any smoke or grease. You might visit a few friends to see how they look in person.

>>"Can someone recommend me a OTR microwave with 12" depth?"No.

For all the reasons GreenDesign just stated, it is a bad idea.

Better to get a shallow mw like the GE model PEM31 Spacesaver II, hang it from a cabinet next to the stove or elsewhere in the room, then put an actual range hood over the stove. That way, you get venting, the ability to keep things working when one device fails (which will most likely be the MW).

However, if you are looking to get a recirculating unit rather than an externally venting one, I would ay you should just skip the OTR unit altogether.

There is nothing wrong with leaving the space unfilled if you cannot get real venting. In the installation manuals that I have seen for 30 inch stoves, many say to leave an open space above the stove of at least 30 inches from stove top to flmmable botttom of the cabinets directly above unless you put something metal in the space (i.e., a hood) to protect the cabinets. Several of the instruction manuals that I have seen recently, severla say you need to have something that metal that projects at least 5 inches beyond the front of the cabinets for fire safety reasons.

If you have vent ducting that you cannot relocate, then get a regular OTR. I believe that there is alt least one OTR that has side-out vents and 400 CFM venting capacity. (Both Nunyabiz and Luv2Putt have posted on this model which I think is an LG. It has a slide-out tray that extneds the meach of the OTR MW venting and pulls about 400 CFM>0

Whether a standard depth OTR will "look good" or not is pretty much a subjective judgment. Some people will hate anything you do with your kitchen, Many people will not look twice at the oTR. Other considerations for me would be: how much do I need to get into the cabinets above the OTR (the projecting oTR will make it harder to reach into the cabinets above it) and how much stuff/goo/etc will accumulate on the flat surface where it projects out and how often do you want to stand on a chair to clean the top or reach innto the upper cabinets. (A range hood will likewise imepede access to the upper cabinets but will aso typically have a slanted front surface that will be easily cleae.

It would be impossible for a OTM to be flush with cabinets unless the door folded down instead of side to side.
They HAVE to stick out at least 3-4" and they look just fine.

Also as mentioned you actually want them sticking out as far as possible to gather as much smoke as possible.
Mine actually has an extension that slides out another 4-6" for that purpose.