Sauté the veggies. Heat oil in a large stockpot over medium-high heat. Add onion and jalapeño, and sauté for 5 minutes, stirring occasionally, until the onion is soft and translucent. Add the garlic and sauté for an additional 1-2 minutes, stirring frequently, until fragrant. Stir in the flour until it is evenly combined and sauté for 1 more minute, stirring frequently.
Simmer. Gradually add in the chicken broth, stirring until combined. Stir in the cooked chicken, green chiles, beans, corn, cumin and oregano. Continue cooking until the soup reaches a simmer, then reduce heat to medium-low and continue simmering for about 5 minutes. Stir in the milk and continue simmering for 5 minutes.
Season. Give the soup a taste, and season generously with salt and pepper as needed.
Serve. Serve warm, topped with your favorite garnishes, and enjoy!