I wanted to cover the same side panels just because they were not looking great. There are unfinished 1/4" panels that will fit between the cabinet face frame and the wall or you can sand smooth, stain and finish the wood already there as long as it is wood and not a veneer. Then install a vent hood to match your appliances. I stained a wood hood with a vent insert to match my cabinets, but that was a more expensive way to go. I did that because I have white appliances, and at the time could not find a white hood I liked.

This is an example of the stained side panel. You will need to cut it down to fit under the hood. I am planning to do the sink sides too at some point.

This picture below shows the panel added to the side by the range:

https://www.houzz.com/photos/my-pics-work-in-progress-phvw-vp~58830972

jhmarie is giving a great example of the right way to do it. If you want an unconventional approach, if you install a stainless steel hood, you could purchase a stainless steel panel that they sell for use as backsplash and then cut it down to two pieces to cover the sides of the cabinets. Here's one of the panels I am talking about:

https://www.lowes.com/pd/Broan-24-in-x-30-in-Stainless-Steel-Metal-Kitchen-Backsplash/1092009

I found those panels at Menards. They already fit between the face frame and the wall width wise. I did need to stain and poly them.

https://www.menards.com/main/kitchen/kitchen-cabinets/all-kitchen-cabinets/quality-one-trade-12-x-30-wall-cabinet-panel/wep12x30wallpnl08033/p-1444451717336-c-14242.htm?tid=4199441703700783216&ipos=12