1 Cut the carrots into very thin slices. Cut the mushrooms into thin slices. Coarsely chop the scallions. Cut the chicken into bite-size pieces; set aside.
2 In a large saucepan, melt the butter over medium heat. Stir in the flour and cook, stirring, until the flour has completely absorbed the butter, about 1 minute.
3 Increase the heat to medium-high, slowly add a small amount of the chicken broth and stir to combine with the butter and flour. Then add the rest of the chicken broth, the thyme and pepper, and bring to a boil, stirring until slightly thickened.
4 Add the pasta and carrots and cook, uncovered, for 3 minutes.
5 Add the mushrooms, chicken and whole tomatoes. Return the mixture to a boil over medium-high 'heat, breaking up the tomatoes with a spoon. Reduce the heat to medium-low, cover and simmer until the chicken is cooked through, about 5 minutes.
6 Stir in the scallions