In a large resealable plastic bag combine 1/4 cup of the flour, the thyme, poultry seasoning, salt, and pepper. Add chicken pieces, half at a time, shaking to coat.

In a large nonstick skillet heat 1 tablespoon of the oil over medium-high heat. Add half of the chicken; cook about 5 minutes or until brown, stirring occasionally. Transfer chicken to a 5- to 6-quart slow cooker. Repeat with the remaining 1 tablespoon oil and the remaining chicken. Add broth, carrots, celery, leeks, and mushrooms to chicken in cooker.

Cover and cook on low-heat setting for 6 to 7 hours or on high-heat setting for 3 to 3 1/2 hours.

If using low-heat setting, turn to high-heat setting. Stir in frozen peas. In a small bowl combine the remaining 1/4 cup flour and the half-and-half; stir into mixture in cooker. Cover and cook about 30 minutes more or until thickened.

Meanwhile, preheat oven to 450°F. Unroll piecrust. Press or roll piecrust into an 11-inch circle; cut into eight wedges. Place wedges on an ungreased large baking sheet. Prick each wedge several times with a fork. Bake for 8 to 9 minutes or until light brown.

To serve, top each serving of chicken mixture with a baked piecrust wedge.