In a mixing bowl, whisk together the flour and salt. Cut in the cold, cubed butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs. Gradually add ice water, one tablespoon at a time, mixing gently until the dough comes together. Shape into a disk, wrap in plastic, and refrigerate for at least 30 minutes.

Preheat your oven to 400°F (200°C). Slice all vegetables thinly and evenly to ensure they cook at the same rate. Toss the zucchini, eggplant, bell peppers, red onion, and tomato in olive oil, oregano, basil, salt, and pepper. If using optional ingredients like sun-dried tomatoes or olives, add them here.

On a lightly floured surface, roll the chilled dough into a rough 12-inch circle. Transfer the dough to a parchment-lined baking sheet. Leaving a 2-inch border, arrange the seasoned vegetables in a circular pattern, slightly overlapping them. Sprinkle with crumbled feta if using.

Carefully fold the edges of the dough over the vegetables, pleating as needed to form a rustic edge. Brush the crust with the beaten egg to give it a beautiful golden color as it bakes.

Bake the galette for 35–40 minutes, or until the crust is golden and the vegetables are tender. Keep an eye on it to ensure the edges don’t overbrown. The aroma of roasted vegetables and buttery crust will fill your kitchen.

Allow the galette to cool slightly on a cooling rack. Garnish with fresh basil before serving. Slice into wedges and enjoy warm or at room temperature.