Preheat the oven to 375 degrees F (190 degrees C).

Heat a large skillet over medium-high heat and stir in sausage. Cook and stir until sausage is crumbly, evenly browned, and no longer pink, about 10 minutes. Drain excess grease.

Separate one egg and set yolk aside; beat egg white and remaining eggs in a bowl. Fold mozzarella cheese, spinach, ricotta cheese, salt, garlic powder, pepper, and sausage into eggs.

Line a 10-inch pie plate with bottom pastry; pour filling into crust. Roll out remaining pastry to fit the top of pie; place over filling. Trim, seal, and flute edges; cut slits in pastry. Beat water and remaining egg yolk in a small bowl; brush over the top of pie.

Bake in the preheated oven until crust is golden and filling is bubbly, 50 to 60 minutes. Let stand 10 minutes before cutting.