You should have a 27” deep hood to begin with. If you’re bumping out the range, the hood will need to be similarly bumped out, with the proper non combustible material to ensure fire safety code is met.

..and when you do that, what goes on the back wall to fill the void on the backsplash?

The proper non combustible material. Usually a custom stainless piece, from a local fabricator. But there is no one size fits all. The solution has to be tailored to the design specifics.

A 2x4, or two 2x4s between the hood and the wall. Then you wrap the exposed wood block edges with stainless steel. I believe Home Depot will cut stainless steel sheet that you buy from them to the size you need to wrap the edges of the wood block.

I found your OP unclear. Why are you bumping out the range, and also, by how many inches? What is going into the space between the back edge of your induction slide-in range and the wall? Will you fill that space in with countertop? If so, the counter needs to be stone, not quartz or corian. Otherwise, head back to HD for another stainless steel strip to put between the back edge of the range and the wall.

You can not have wood in the combustible zone, even if covered with a non combustible material. The entire assembly would need to meet the vertical clearance for combustibles over the cooking zone. Usually a minimum of 30” clearance.

I really dont understand either of you. The photo is what I mean by a bump out.

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A bump-out of a range means it sits forward, it is pushed forward or "proud", from the cabinets on each side. To do that means you'd need a strip of some non-combustible material behind the back edge of the range to fill in the amount of space you've bumped out/pushed it forward. See photos below. If you are talking about something else, please explain better. That photo you posted has so much going on I cannot tell which part of it you are talking about - explain in words.

That photo with a range (not a cooktop) comes out a few inches more then the base cabinets. The spice pull out legs on either side begins the bump out. Am I clear now?

Heat destroys spices / herbs / oils, always store those items in a cool, dark spot.

In general, the center of the entry aperture into the hood (front-to-back) should be aligned with the center of the area occupied by burners or hobs. Note that due to lights and controls, the center of the entry aperture is often not the front-to-back center of the hood. In many wall hoods of sufficient front-to-back depth, this is not an issue; close enough is perfect. Otherwise any gap at the rear has to be blocked with appropriate materials as noted above as influenced by hood height over the burners. A horizontal plate may work given cabinets at the sides. A sloped plate directing effluent into the aperture can aid plume capture under some conditions.

Some of the higher end manufacturers (e.g. ModernAire) build hoods to order. You tell them exactly what size you want and that's what they'll build. No need for extra fillers