Heat oven to 375°F. Bake biscuits as directed on can.*
Meanwhile, melt margarine in large skillet over medium-high heat. Add bell pepper and celery; cook and stir 1 minute. Add flour, bouillon and thyme; cook and stir until mixture is smooth and bubbly. Gradually add milk, cooking until mixture boils and thickens, stirring constantly. Stir in chicken, peas, mushrooms and pimientos. Cook until thoroughly heated.
To serve, split warm biscuits; place bottom half of biscuit on each plate. Spoon hot chicken mixture over each. Top with remaining biscuit halves.