In a large bowl stir together the flour, instant yeast, and fine salt. Pour in the warm water and 3 tablespoons of the olive oil. Stir with a spoon or your hand until a sticky, shaggy dough comes together and no dry flour remains at the bottom. It will look messy and that is fine. Cover the bowl with plastic wrap or a damp kitchen towel and let it sit at room temperature for 1 to 2 hours, until the dough has roughly doubled and looks puffy with bubbles on the surface.

While the dough rises, prep the zucchini. Slice it into rounds about 1/8 inch thick, lay them on a clean kitchen towel or several layers of paper towels, and pat the tops dry. Press gently to draw out moisture. Let them sit and dry while the dough finishes rising. Skipping this step can cause soggy patches on the finished focaccia.

Pour 2 tablespoons of olive oil into your baking pan and tilt it around so the entire bottom surface is coated generously. Scrape the risen dough into the center of the pan. Using oiled fingertips, gently press and stretch the dough toward the edges. If it keeps springing back, let it rest for 5 minutes, then try again. Work slowly and it will eventually cover the pan in an even layer about 3/4 inch thick.

Arrange the zucchini slices over the top of the dough in slightly overlapping rows or circles, covering most of the surface. Scatter the fresh thyme or oregano over everything. Drizzle the top evenly with the remaining olive oil, then finish with the flaky salt and black pepper. Let the topped dough rest uncovered for 20 minutes while you heat the oven to 425 degrees F.

Use your fingertips to dimple the surface of the dough all over, pressing firmly down without going all the way through. This creates the classic focaccia texture and keeps the toppings in place during baking.

Bake on the center rack for 22 to 25 minutes. The focaccia is ready when the edges are deep golden brown, the zucchini looks slightly blistered and tender at the edges, and the bottom of the bread is golden when you lift one corner with a spatula. The center should feel set and not doughy when you press it lightly.

Transfer the pan to a wire rack and cool for at least 10 minutes before cutting. You can slide the focaccia onto a cutting board and cut it into squares or rectangles with a serrated knife. Serve warm or at room temperature.