Look for canned pineapple slices. Shy away from pineapple chunks or tidbits, as they'll get messy (unless you want to make a pineapple salsa to use as a burger topping, which we fully support).

Stir the pineapple and 2/3 cup picante sauce in a medium bowl. Thoroughly mix the beef and the remaining picante sauce in a large bowl. Shape the beef mixture into 4 (1/2-inch-thick) burgers.