01 - In a large mixing bowl, combine the all-purpose flour, instant yeast, and fine sea salt. Pour in the warm water and 3 1/2 tablespoons of extra-virgin olive oil. Stir with a wooden spoon until a sticky, cohesive dough forms.
02 - Knead the dough gently directly in the bowl for 1 to 2 minutes. Cover tightly with plastic wrap or a damp kitchen towel. Place in a warm, draft-free spot and let rise for 1 to 2 hours, until the dough 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. Simmer gently for 10 minutes, stirring occasionally, then remove from heat and let cool.
04 - Coat a large baking sheet (approximately 12x16 inches) generously with olive oil. Turn the risen dough onto the prepared sheet. Using oiled fingers, gently stretch and press 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), positioning the rack in the center.
06 - Dimple the surface of the stretched dough firmly with your fingertips. Drizzle lightly with additional olive oil. Pre-bake for 10 minutes until the crust is just set but not yet browned.
07 - Remove the partially baked focaccia from the oven. Spread the cooled pizza sauce evenly across the surface. Scatter the shredded mozzarella in an even layer, then arrange the pepperoni (if using), sliced red and green bell peppers, red onion, black olives, and mushrooms over the cheese. Season with freshly ground black pepper.
08 - Return the topped focaccia to the oven and bake for 15 minutes, or until the cheese is fully melted and bubbling and the crust edges are deep golden brown.
09 - Let the focaccia stand for 5 minutes to set. Sprinkle with chopped fresh basil, cut into squares, and serve warm.