Ideas for filling up large nook
If you just want countertop the whole way, they can be spliced/jointed. The fancy stuff by fancy installers with fancy glues can approach a seamless appearance (for fancy prices) while typical sheet goods will have a visible seam, which is not a big deal if fancy prices don't appeal. Depending on the purpose of the countertop you could do something like hide the seam under a built-in/on cutting board.

Then again, perhaps you need a basement fridge or freezer, 3 feet taken care of easily.

This slides off towards (off-topic) decorating advice pretty quickly once you get out of the "how to do the whole length as countertop" question which is somewhat on-topic.

Replace the light with a junction box for your new lighting.