Answer:
What is as big as you are and yet does not weight anything?
A time when they're green. A time when they're brown. But both of these times, cause me to frown. But just in between, for a very short while. They're perfect and yellow. And cause me to smile.
My first is an insect; my second is a border; my whole puts the face in a tuneful disorder.
Face with a tree, skin like the sea. A great beast I am. Yet vermin frightens me.
In the evening I'm long, in the morning I'm small; When seen in a ballroom, I'm nothing at all.
This food is a tortilla filled with cheese and sometimes chicken before being heated or cooked.