Preheat the oven to 350°F (175°C).

In a medium saucepan, melt 1 tablespoon of margarine.

Add 3 tablespoons of flour and stir over medium heat for 1 minute, being careful not to brown the flour.

Gradually add the chicken stock and skim milk, whisking constantly until the mixture comes to a boil.

Continue to cook for 1 minute more, then set aside.

In a large skillet, melt the remaining tablespoon of margarine along with canola oil over medium heat.

Add the chicken breasts and cook until browned on both sides, about 5 minutes per side.

Remove the chicken from the skillet and place in a baking dish coated with non-stick vegetable spray.

In the same skillet, cook the sliced mushrooms for 5 minutes.

Stir in the remaining tablespoon of flour, the white wine, and water into the skillet with the mushrooms.

Simmer, stirring, until the sauce thickens, about 10 minutes.

Stir in the 2% milk, salt, tarragon, garlic powder, and black pepper.

Pour the sauce over the chicken in the baking dish.

Bake, uncovered, until the chicken is hot and cooked through, about 45 minutes.

Sprinkle the cooked dish with chopped green onions and parsley.

Bake for an additional 5 minutes.