Just a piece of stainless steel there. Have a company bend it so it is the same depth/thickness as the marble. It will look like it was supposed to be there.

If that is marble and not quartz you probably don't want it behind the stove where it could get very splattered, dirty and etched. You could do a stainless panel from counter to hood just behind the stovetop. If you do a tile, it might look best from counter behind stovetop to hood.

Looks like an oops. Which it is. Remove it and do stainless from bottom to top.

There is no workaround for this. You have spent good money on this kitchen. Take that slab out and put tile or stainless back there.

Do a stainless steel panel with a shallow 3-4" stainless steel shelf. This is salvageable....but gotta weigh out the costs and pros/cons.

IMO no matter what you add it will be wrong a shelf will be too high to be useful a hunk of stainless where it would never really be needed . IMO if you want this material get a slab do it right and use the marble left over if carefullty removed for an end table or small vanite or whatever. Who did the design and measuring?

I agree with The Kitchen Place-

The stainless with possible shelf as @thekitchenplace suggested. That will look like it was planned and function well.

If you do the stainless steel shelf, pull the panel out to the same level as the slab.

Stainless will look fine.

cut out a U (with straight corners) in the slab above the range so that it still provides some of the backsplash and looks more intentional in design. Fill open space inside U and then through top of hood with backsplash.

putting a completely different material pieced in above it will look like you're covering a mistake. either spring for the extra piece,,,or,,

is there anyway they could recess that spot? even a little? then maybe it would look like it's meant to be there. you could line it copper sheeting or tile,,,

Stainless the entire section over the range or replace the entire wall.. And call the idiots who "helped "you determine how much material you needed to do the task at hand. If you purchased from a slab yard, and were armed with a kitchen plan and elevation, and all dimensions? I would make them pay. There is ZERO excuse to discover this at INSTALL. Repeat ZERO.

The photos of the recesses drive me nuts. Never, ever, ever store spices, oils, or wine near the heat of a stove and oven. Everybody (except, apparently, those designers) knows that.