01 - In a large mixing bowl, whisk together the all-purpose flour, instant yeast, and fine sea salt. Pour in the warm water and 3 ½ 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 begins to smooth out. Cover tightly with plastic wrap or a damp kitchen towel. Set in a warm, draft-free spot and let rise for 1 to 2 hours, or until the dough has doubled in bulk.
03 - While the dough rises, heat 1 tablespoon of olive oil in a small saucepan over medium heat. Add the minced garlic and sauté until fragrant, about 30 seconds. Stir in the passata, dried oregano, salt, and sugar. Reduce the heat to low 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, positioning the rack in the center.
06 - Dimple the surface of the stretched dough all over with your fingertips. Drizzle lightly with additional olive oil. Pre-bake for 10 minutes until the dough is just set but not yet browned.
07 - Remove the par-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 sliced pepperoni (if using), red and green bell peppers, red onion, black olives, and mushrooms over the top. Finish with a generous crack of black pepper.
08 - Return the assembled focaccia to the oven and bake for an additional 15 minutes, or until the cheese is fully melted and bubbly and the edges are deep golden brown.
09 - Remove from the oven and let stand for 5 minutes to allow the cheese to set. Sprinkle with chopped fresh basil, cut into squares, and serve warm.