Cut chicken into small bite-size pieces. Coat the bottom of a Dutch oven or large pot with two tablespoons vegetable oil and place over medium-high heat. Add chicken and saute for 4 to 5 minutes, or until nicely browned. While cooking, season with 1/2 teaspoon salt and fresh ground black pepper, to taste. Remove from heat and use a slotted spoon to transfer chicken to a plate. Set aside.
Meanwhile, rinse and drain one can of cannellini beans, transfer to a small bowl and lightly mash with a potato masher or the back of a spoon. Set aside. Rinse and drain remaining can of cannellini beans and pinto beans (do not mash) and set aside.
Return pan to medium heat and add onion and peppers. Cook, stirring frequently, for several minutes until softened. Add 1 teaspoon minced garlic and cook, stirring, for another minute. Season the vegetable mixture with remaining 1/2 teaspoon salt, fresh ground black pepper, 2 teaspoons chili powder, 2 teaspoons ground cumin, 1 teaspoon ground coriander, and 1 teaspoon oregano. Cook and stir for a minute or two or until fragrant. Add chicken broth, mashed beans, whole beans, and the browned chicken, stirring well to incorporate the mashed beans. Increase heat to high and bring mixture to a boil. Reduce heat to low, cover the pot, and simmer for 20 to 30 minutes.
In a small bowl or measuring cup, combine milk with cornstarch. Stir into chili and simmer over low heat until thickened.
Serve with optional toppings and tortilla chips.
Loosely adapted from Taste of Home