To prepare burgers, combine the first 10 ingredients in a large bowl. Add pinto beans and corn; partially mash with a fork. Divide bean mixture into 4 equal portions, shaping each portion into a 3 1/2-inch patty, and refrigerate for 10 minutes.
To prepare chipotle mayonnaise, combine mayonnaise and 1 teaspoon chipotle in a small bowl; set aside.
Heat canola oil in a large nonstick skillet over medium-high heat. Add patties to pan, and cook 4 minutes on each side or until thoroughly heated. Place patties on bottom halves of buns; top each patty with 1 tablespoon mayonnaise, 1 lettuce leaf, and top half of bun.