Broil croissant halves 2 – 5 minutes, or until golden. Meanwhile slice veggies (I've found it easiest to get veggies from supermarket salad bar than to buy whole vegetables, slice them, and just use some of the slices).
Pile the veggies on the sandwich: lettuce on bottom, tomato, avocado, cucumber, onion, sprouts on top. Top with other croissant half. Hold sandwich together in 1 or two places by sticking a toothpick pierced with an olive.