We apologize for the delay in responding. This plant looks like Lambsquarter, a fairly common weed. As an annual, it will die out on its own this coming winter, but before then it should be removed or at least cut back repeatedly so it does not produce seed that could germinate the following spring. Covering any exposed soil with mulch or landscape fabric will help prevent other weed seeds from germinating going forward. (If the weeds came up while the bed was fallow and not yet planted with summer vegetables, using a cover crop next season may help act like a "living mulch" to similarly discourage weed seeds from sprouting. Our Cover Crops for Gardens page has more information if you are interesting in using them in the future.

Miri