In a large saucepan or Dutch oven, heat about 1 teaspoon of olive oil over medium-high heat. Throw in the carrots, celery, and onion and sauté until slightly softened and onions begin to look transparent. Add in reconstituted broth, water, rice, and the seasoning packet that is included with the rice. Stir and bring to a simmer. Reduce heat to low and simmer for at least 30 minutes (or whatever is recommended on the package of rice). In a separate small pan, melt your butter. Stir in flour and salt and pepper. (I didn’t add any salt at this stage because I knew the seasoning packet for the rice probably had plenty of salt in it.) Slowly add the milk, whisking to eliminate clumps. Stir this mixture into the rice and vegetable mixture. Add your cooked chicken and cook until heated through (10-15 minutes).