Bigger than an ordinary salad. Elaine in Seinfeld would often order it.
George: What's in the BIG salad?
Jerry: Big lettuce, big carrots, tomatoes like volleyballs.
When someone wants credit for something when it is or isn't really credit-worthy. Or is credit worthy and they call attention to their credit-worthy performance.
"What was it dude, a big salad?"
My husband said I thanked everyone at the table for dinner but him. He cooked the meal but everyone chipped in. He asked me, "Don't I get a thank you?", to which I replied, "What was it - a big salad?"