from How To Cook Everything Vegetarian by Mark Bittman

2 cups well-cooked white, black or red beans or chickpeas or lentils, or one 14-ounce can, drained
1 medium onion, quartered
1/2 cup rolled oats (preferably not instant)
1 tablespoon chili powder or spice mix of your choice
Salt and freshly ground black pepper
1 egg
Bean-cooking liquid, stock or other liquid (wine, cream, milk, water, ketchup, etc) if necessary
Extra virgin olive oil or neutral oil like grapeseed or corn, as needed

Combine the beans, onion, oats, chili powder, salt, pepper and egg in a food processor and pulse until chunky but not pureed, adding a little liquid if necessary (This is unlikely, but not impossible) to produce a moist but not wet mixture.  Let the mixture rest for a few minutes if time allows.

With wet hands, shape into whatever size patties you want and again let rest for a few minutes of time allows. (You can make the burger mixture or even shape the burgers up to a day or so in advance.  Just cover tightly and refrigerate, then bring everything back to room temperature before cooking.)  Film the bottom of a large nonstick or well-seasoned cast iron skillet with oil and turn the heat to medium.  A minute later, add the patties.  Cook until nicely browned on one side, about 5 minutes; turn carefully and cook on the other side until firm and browned.

Beans Quick and Easy Cooking Vegetarian