I've been mulching our vegetable gardens for decades as it is so beneficial. In fact I just finish spreading 28 cu.yards this past weekend.

It's great for moderating soil temps, moisture retention & suppressing weeds/grass. Plus, it is a great way to add organic material to build soil structure.

It depends on what he mulched it with...

Even if he did mulch it with something that I would assume is not poisonous to you via touch or smell, you can just remove it and grow there this season.

However, if you want a better answer, then we will need to know what he mulched with and how long it has been there.

The answer for your mulch problem does depend on what that mulch is and whether it flies in the face of your organic gardening rules and limits, if any. For the most part mulch is not a problem at all.

Mulch is an insulator for moisture and temperature. It should be a dry thing except for rainy times and it is nearly inert. If it is really "mulch" and not a soil amendment (dug or scratched in), and especially if it's an airy mulch like straw and not a dense one like sawdust or bark, it's interaction with the growing soil is very minimal.