Youre tile guy's fault,he still gets blamed ??? he didnt preplan for this years ago???? hmmmmmm

You can do 2 things. Use a diamond blade on angle grinder and VERY CAREFULLY scribe cut the tile off. ( very hard to do with cabs in place and not damage them as well as a perfect cut.)

easier remedy is to use a table saw and rip furring strips the exact thickness of the tile to wall differential. ( IE thickness of tile and mortar likely around 3/8-1/2")

use those strips to glue/screw in place over the studs in the wall and behind vertical bracket mounts. This will incur a "protruding" look when microwave installs.

-best

Time for an updated backsplash. Rip all that pink travertine down, install a new splash, and then the new OTR.

Is the problem that the bracket will not mount flat because of the tile sticking out? Could you just use wooden shims the depth of the tile to even the surface, or does that cause a front-back spacing issue?

You could use a diamond blade on an angle grinder to cut the tile back. It would be dusty, but should go fairly quickly.

I've installed two over the counter MW's and they both used a an upside down U-shaped housing that mounted to the top and to the back wall. IIRC they were designed to hold most of the weight on the wall. Once the housing was mounted, the microwave just slide into it like file drawer.

Bruce

Use furring strips, shims or even washers behind the fastener locations on the brackets.
I think if you cut the tile, you may have a problem mounting the micro box with the wall bracket being recessed beyond the tile, so check mounting instructions carefully.

Exactly.

To cut the the tile in place you could use a diamond blade on a grinder, or in a pinch a blade on a multi-tool.

Or furr the wall out with a piece of ply of the appropriate thickness screwed into the studs.

Tundra- to clarify, it was the three tiles that were left uncut (slid them back behind microwave so he didn't have to cut them) that caused the issue of mounting. I would certainly not expect a tile guy to predict future mounting plates, I was only dissatisfied that he could have cut them all same, grouted all same, and we would have not had this issue. I appreciate your advice though!

A huge thank you to everyone for your helpful advice! We did end up placing mounting blocks behind microwave and it worked well. Thank you for sharing your time and knowledge with me! Appreciate it!

You are welcome