Please help with this riddle!

Hey, can anyone help with the solution of this riddle, it's tricky but here you go;

My first's simply a vegetable, delicious, round and green.
My third and fourth are sound asleep, as plainly can be seen.
My fifth is fifty, clear enough for any riddle-setter.
Two of my second on their sides will give my final letter.
Now that my second has my parts, fit them together well
You see me now before your eyes, it's plain for all to tell.

There, please help asap! Thanks, dan!