My first thought was it looks like a pepper plant :)

looks like some kind of amaranth.

Upon closer inspection the leaf pattern is different than a pepper plants. :/

I think it is NOT a common weed. But not pepper or tomato. Amaranth could be a possibility. They are fast growing.
Interesting to keep it a while until you know what it is.

Pull one up and see if it has pink roots. That would make it a red rooted pigweed, which is a wild amaranth. Weed with redeeming qualities.

Pigweed.