Heat a large, deep nonstick skillet, that has been sprayed with cooking
oil spray, over moderately high heat. Season the chicken with 1/4 teaspoon
each of the salt and pepper and add to the pan. Cook until browned, turning,
about 8 minutes in all. Remove and keep warm.
Add the margarine to the pan and reduce the heat to moderately low. Add
the onion and cook, stirring occasionally, until translucent, about 5
minutes. Raise the heat to moderately high. Add the mushrooms, garlic,
and 1/4 teaspoon of the salt. Cook, stirring frequently, until the vegetables
are browned, about 5 minutes.
Add the flour and cook, stirring, for 30 seconds. Stir in the vermouth
and bring back to a simmer. Stir in the broth, tomatoes, thyme, and the
remaining 1/2 teaspoon salt. Add the chicken and any accumulated juices.
Reduce the heat; simmer, covered, until the chicken is done, about 10
minutes. Stir in the parsley and the remaining 1/4 teaspoon pepper.