Preheat oven to 350°F.
Prepare the rice according to package instructions and set aside. Saute onions, peppers, and mushrooms in oil and set aside.
Combine all ingredients except 1 cup of cheese and pie crust, into large bowl and mix well. Pour into greased 9-inch glass pie plate. Top with remaining 1 cup of cheese and set aside.
Roll out pie crust, cut into 1/2-inch wide strips and cover dish in lattice design, then brush dough lightly with egg.
Place in 350°F oven for 30 minutes, when top is golden brown, remove, let cool, and enjoy.
This dish is an excellent way to use holiday turkey leftovers, plus it freezes well.