In a large bowl, combine 1.5 cups warm water, 2.25 teaspoons active dry yeast, and 1 teaspoon granulated sugar. Stir gently and let sit 5–10 minutes until foamy.
Add 3.5 cups all-purpose flour, 2 teaspoons salt, and 2 tablespoons olive oil to the yeast mixture. Stir until a shaggy dough forms.
Turn dough onto a lightly floured surface and knead 5–7 minutes until smooth and elastic. Add a little flour if too sticky.
Lightly grease a clean bowl with olive oil. Place dough inside, turning once to coat. Cover and let rise in a warm spot 1–1.5 hours until doubled.
While dough rises, make the sauce: in a small bowl, combine 15 ounces crushed tomatoes, 2 minced garlic cloves, 1 teaspoon dried oregano, 0.5 teaspoon dried basil, 0.25 teaspoon salt, and 0.125 teaspoon black pepper. Stir and set aside.
Prepare toppings: shred 8 ounces low-moisture mozzarella, slice 3 ounces pepperoni, 0.5 cup mushrooms, 0.5 green bell pepper thinly, and 0.25 small red onion thinly.
Preheat oven to 475°F with pizza stone or steel inside for at least 30 minutes. If unavailable, use a baking sheet.
Punch down risen dough and divide in half. On a floured surface or parchment, stretch one half into a 12-inch circle. Transfer to preheated stone or sheet.
Spread half the sauce over dough, leaving a 0.5-inch border. Sprinkle half the mozzarella, then arrange half the pepperoni, mushrooms, bell pepper, and red onion. Brush crust with olive oil if desired.
Bake 12–15 minutes until crust is golden and cheese is bubbly with spots of browning.
Let pizza cool on a rack a few minutes before slicing. Repeat assembly and baking with the second half of dough and toppings. Serve hot.