Mushroom Zucchini Pie
["1 c. chopped onion", "3/4 lb. mushrooms, sliced", "3/4 lb. zucchini, sliced", "1/4 c. butter or margarine", "2 Tbsp. flour", "1 tsp. salt (optional)", "1/4 tsp. pepper", "1/4 tsp. thyme", "1 pkg. pie crust mix", "1 egg yolk", "1 Tbsp. water"]
["Saute onion, mushrooms and zucchini until tender-crisp, about 5 minutes.", "Drain and add flour, salt, pepper and thyme.", "Mix to coat.", "Remove from heat.", "Preheat oven to 375\u00b0."]
["onion", "mushrooms", "zucchini", "butter", "flour", "salt", "pepper", "thyme", "pie crust", "egg yolk", "water"]