01 - In a large mixing bowl, combine the all-purpose flour, instant yeast, and fine sea salt. Pour in the warm water and 3½ tablespoons of extra-virgin olive oil. Stir with a wooden spoon until a sticky, shaggy dough comes together.
02 - Knead the dough gently directly in the bowl for 1 to 2 minutes until it becomes slightly smoother. Cover tightly with plastic wrap or a damp kitchen towel. Place in a warm, draft-free spot and let the dough rise for 1 to 2 hours, or until it has doubled in volume.
03 - While the dough rises, heat 1 tablespoon of olive oil in a small saucepan over medium heat. Sauté the minced garlic until fragrant, about 30 seconds. Stir in the passata, dried oregano, salt, and sugar. Reduce the heat and simmer for 10 minutes, stirring occasionally. Remove from heat and let cool.
04 - Generously coat a large baking sheet (approximately 12x16 inches) with olive oil. Turn the risen dough out onto the prepared sheet. Using oiled fingertips, gently press and stretch the dough toward the edges. If the dough resists, let it rest for 15 minutes before continuing to stretch.
05 - Preheat the oven to 425°F (220°C), ensuring the rack is positioned in the center.
06 - Press deep dimples across the surface of the dough using your fingertips. Drizzle lightly with additional olive oil. Bake for 10 minutes, just until the crust is set but not yet browned.
07 - Remove the par-baked focaccia from the oven. Spread the cooled pizza sauce evenly over the surface. Scatter the shredded mozzarella, then arrange the pepperoni (if using), sliced red and green bell peppers, red onion, black olives, and mushrooms. Finish with freshly ground black pepper.
08 - Return the topped focaccia to the oven and bake for an additional 15 minutes, or until the cheese is fully melted and bubbly and the crust edges are deep golden brown.
09 - Let the focaccia pizza stand for 5 minutes to set. Sprinkle with chopped fresh basil, cut into squares, and serve immediately.