looks like an oil seed rape plant, or some other brassica like mustard. I sometimes get them from the bird seed.

It's leaves do look cabbage like.

Looks like one of my brussel sprouts with a yellow flower.

My first thought was a Brussels Sprout gone to seed, then I thought of 'Nero Toscana' Kale, which matches the leaf shape and color better. Rapeseed is also a possibility, but the varieties grown here in Arizona are darker green and more lobed.