It's a DISH!!! That's how a Brazilian would FIRST translate! We use "prato" meaning dish much more than plate. Ex: What's your favorite dish? -> Qual seu prato favorito?
The OBJECT PRATO is PLATE.
The favorite DISH is also called Prato.
But dishes are broader. You can wash the dishes, and that would be washing more than just plates. In that case DISHES is LOUÇA.
That was my thinking based on Spanish: Primero plato = First course.
prato = plato in Spanish? In the context of primero plato, segundo plato?