It's like a brick of deep fried onion ring goodness... Imagine, a house made of Onion Ring Bricks! *drooools*
[Update:] Turns out this is called the Tony Roma's Onion (full or half) Loaf. (Link to their Menu)
From an Anonymous commenter: Basically they fill those deep-fry baskets you normal see filled with french fries cooking in the deep fryer, but instead fill it with battered onion rings.