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

Make dough: Combine 1 cup flour, yeast, sugar, and salt in a large bowl. Add very warm water and oil; mix until well blended, about 1 minute. Gradually add enough remaining flour to make a soft, slightly sticky dough ball. Knead on a floured surface, adding more flour if needed, until smooth and elastic, about 4 minutes. Cover and let rest on the floured surface.

While dough rests, make filling: Cook and stir sausage in a large skillet over medium-high heat until crumbly and browned, 5 to 7 minutes. Use a slotted spoon to remove sausage to a paper towel-lined plate to drain; discard grease from the skillet. Add spinach and water to the skillet; sauté over medium heat until spinach is wilted, 1 to 2 minutes; drain liquid. Return sausage to the skillet with spinach. Set aside.

Combine ricotta, mozzarella, and egg in a mixing bowl. Stir in Italian seasoning, crushed red pepper, and garlic salt; set aside.

Divide dough into 4 equal pieces. Roll 1 dough piece into an 8-inch circle on a floured surface. Spread about 1/3 cup ricotta mixture over the bottom half of dough, leaving a 1/2-inch border. Top with heaping 1/3 cup sausage-spinach mixture. Fold the top half of dough over filling. Pull the edge of the lower crust over the top; fold and press layers together to seal. Transfer to a greased baking sheet; cut 3 to 4 vents on top. Repeat with remaining dough.