01 - In a large mixing bowl, combine the flour, instant yeast, and fine sea salt. Pour in the warm water and 3 ½ tablespoons of 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. Set in a warm, draft-free spot and let rise for 1 to 2 hours, or until doubled in volume.
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 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 springs back, let it rest for 15 minutes before continuing to stretch.
05 - Preheat the oven to 425°F, positioning the rack in the center.
06 - Using your fingertips, press deep dimples across the surface of the dough. 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 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 assembled focaccia pizza to the oven and bake for 15 minutes, or until the cheese is fully melted and bubbly and the edges are deep golden brown.
09 - Allow the focaccia pizza to stand for 5 minutes before slicing. Sprinkle with chopped fresh basil, cut into squares, and serve warm.