Place chicken between 2 sheets of plastic wrap; pound with a mallet to 1/2-inch thickness. Combine cumin with cayenne pepper and rub over chicken. Heat oil in a large skillet over medium heat. Sauté chicken for 4 minutes per side. Remove to a cutting board. Return the skillet with pan drippings to medium heat. Add the onion and jalapeño and cook, stirring, 1 minute. Add the beans, corn, tomatoes, and 3 tablespoons water and cook, stirring, 1 or 2 minutes, until ingredients are just heated through. Remove from heat and toss with the scallions, cilantro, and vinegar. Season to taste with salt and freshly ground pepper. Slice chicken and arrange on top of beans.