Cut the chicken into small bite-size pieces. Coat the bottom of a Dutch oven or large pot with two tablespoons canola or vegetable oil and place over MEDIUM-HIGH heat. Add the chicken and sauté for 4 to 5 minutes, or until nicely browned. While cooking, season with ½ teaspoon salt and freshly ground black pepper, to taste. Remove from the heat and use a slotted spoon to transfer the chicken to a plate and set it aside.
Meanwhile, rinse and drain one can of cannellini beans, transfer them to a small bowl and lightly mash with a potato masher or the back of a spoon. Set aside. Rinse and drain the remaining can of cannellini beans and pinto beans (do not mash) and set them aside.
Return the pot to MEDIUM heat and add the 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, freshly ground black pepper, chili powder, cumin, coriander, and oregano. Cook and stir for a minute or two or until fragrant. Add the chicken broth, mashed beans, whole beans, and the browned chicken, stirring well to incorporate the mashed beans. Increase heat to HIGH and bring the mixture to a boil. Reduce the 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 the mixture into the chili and simmer over LOW heat until thickened.
Serve with optional toppings and tortilla chips.