Combine flour, yeast, and salt in a large bowl. Combine olive oil and water and whisk into dry ingredients. Continue to stir and mix until a cohesive ball of dough forms.
Turn dough out onto a lightly floured surface and knead until dough is smooth and only slightly tacky to the touch. If dough is overly sticky, knead in 1-2 tablespoons flour.
Place dough in a greased bowl, cover, and let rise in a warm place until doubled, about 1 hour.
Preheat oven to 450°F and line two baking sheets with parchment or silicone baking liners.
Deflate dough and divide into 6 pieces. Roll out each piece to about 8 inches diameter.
On one half of each dough, place a spoonful of pizza sauce, then some pepperoni, then some cheese, making sure to leave 1/2 inch edge.
Brush water around the edge of the dough. Fold other side of dough over and pinch edges to seal, creating a decorative fold if you like. Repeat with remaining ingredients. Use a spatula to transfer the calzone to the baking sheet.
Bake calzones for about 12 minutes, rotating pans halfway through.
Notes
Use more or less fillings as desired.
If you like, brush the tops of the calzones with egg wash before baking and sprinkle on parmesan cheese and/or Italian seasoning.