1 1/2 cups unsalted chicken stock, divided 2 (15-oz.) cans unsalted Great Northern beans, rinsed, drained, and divided 2 tablespoons olive oil 1 cup chopped yellow onion 1 tablespoon minced garlic 1 1/2 teaspoons all-purpose flour 1 tablespoon ground cumin 2 (4-oz.) cans mild chopped green chiles, drained 1/2 teaspoon black pepper, divided 1/4 teaspoon kosher salt 8 ounces boneless, skinless rotisserie chicken breast, shredded (about 1 cup) 2 tablespoons fresh lime juice 1/4 cup sliced radishes 2 tablespoons light sour cream 2 tablespoons fresh cilantro leaves 1 ripe avocado, sliced