600ml aluminium one height bento box

I'm looking for bento boxes that have only one tier and that are about 500-600ml. My preference would go for a metal one. But, this isn't the most important thing. Just one tier bento would definitely be great. I just cannot create in these two tier bento boxes and the tupperware and lock and lock you can find are about 700ml and quite high in comparison to bento boxes. Any tips?