01 - In a large mixing bowl, combine the flour, instant yeast, and fine sea salt. Pour in the warm water and 3½ tablespoons of olive oil. Stir with a wooden spoon until a sticky, shaggy 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 set aside to cool.
04 - Coat a large baking sheet (approximately 12x16 inches) generously with olive oil. Turn the risen dough onto the prepared sheet. Using oiled fingertips, gently stretch and press the dough toward the edges. If the dough resists, let it rest for 15 minutes before continuing.
05 - Preheat the oven to 425°F, positioning the rack in the center.
06 - Dimple the surface of the dough firmly with your fingertips and drizzle lightly with additional olive oil. Bake for 10 minutes until the crust is just set but not yet browned.
07 - Remove the par-baked focaccia from the oven. Spread the pizza sauce evenly across the surface. Layer on the shredded mozzarella, then arrange the pepperoni if using, sliced bell peppers, red onion, black olives, and mushrooms. Season with freshly ground black pepper. Return to the oven and bake for 15 minutes, until the cheese is fully melted and the edges are golden.
08 - Allow the focaccia to stand for 5 minutes before slicing. Sprinkle with chopped fresh basil, cut into portions, and serve warm.