I would a wide horizontal piece of art. I think you need some color for interest in your room. All depends on what you like.

Are there stools tucked under the counter and do people sit at the island? Why are the chairs against the wall? How much distance is there from island to the wall and are you concerned people will bump into framed artwork?

Framed Audubon prints would look great in here. This pic reminds me of them and I used to have a large one in my kitchen.

Ansley Park Transitional Kitchen · More Info

The stools are just there for when we have more people over. Unfortunately the way they designed the kitchen , they made the island too big and they didn't account for stools on the island without the sink so there is no overhang. The large wall was going to be taken down but it was a supporting wall and it became too complicated affecting too many things to remove it. It's so large so it needs to look "good" since I can't have cabinets or shelves on it

Options for the walls. There are scores of options that can work on your wall.

A mural of a map of a city

There are lots of peel and stick murals

Black and white landscape murals