What is this plant growing in my herb container?

[daisy01]

I have a "weed" growing in my herb container. I let it grow because I was curious what it was. It reminds me of cucumber or courgette but I'm not sure. The leaves are waxy in texture. It's the plant circled (the other seedling is oregano which I planted myself). I was also wondering whether my herb container was a bit crowded? I'm not sure how much space herbs need. It's a 60cm container with coriander, oregano, parsley, dill, basil, thyme, sage and chives. I know I'll have to transplant them all eventually.

[ameno]

It looks like a brassica of some sort, maybe kale.

[Jungle Jane]

You could take it out & put it in a pot,I don’t know what it is but your herb pot looks really good how it is.

[daisy01]

I haven't planted any brassicas outside this year but I suppose a seed might have been in the compost or dropped by a bird. I will move it to another pot and see what it grows into.