That's a Slug. Serious night-feeder that hides during the day under mulch or frankly anything on the ground that provides good hiding space. There are quite a few remedies out there depending on how organic you want to go. Small containers (like jar lids) filled with beer attract & then drown them. Some folks swear by spreading ground barriers of Diatomaceous Earth or even crushed eggshells around plants, since it's considered that the slugs don't like to crawl across it. There's also a commercially-available product called "Sluggo" (https://www.pestproducts.com/sluggo.htm
) that's supposed to be very effective. You may need to experiment to see what works best for you.
My body is a temple. Unfortunately, it's a fixer-upper.