In a large bowl, stir together the oil, garlic, cumin seeds, sesame seeds, mustard seeds, Aleppo pepper, and salt.

Slice the cauliflower into slabs ¼ inch (6 mm) thick, letting any smaller pieces naturally separate, then cut into bite-size pieces. If using cabbage, slice through the core into 1-inch (2.5 cm) wedges.

Gently toss the cauliflower, chickpeas, and dates in the large bowl to coat in the spiced oil.

Preheat the oven to 425°F (220°C) with a rack positioned in the center. Line a sheet pan with parchment paper.

Roll the dough into a round and set it on the lined sheet pan using the Basic Method.

Arrange the filling over the crust, leaving a 2-inch (5 cm) border. Fold the edges of the filling toward the center, overlapping and pleating as desired.

Freeze the galette on the sheet pan for 10 minutes.

Remove the galette from the freezer and brush the egg wash over the exposed crust.

Bake until the crust is starting to turn golden, 12 to 15 minutes.

Reduce the oven temperature to 375°F (190°C) and continue to bake until the filling is browned and the crust is deeply golden brown, another 40 to 50 minutes, rotating the sheet pan front to back halfway through.

Remove the galette from the oven and cool, uncovered, for 15 minutes or up to 8 hours.

Slice and serve, topped with mint.

Without the mint, leftovers can be stored in an airtight container in the refrigerator for up to 3 days. Reheat on a sheet pan in a 350°F (180°C) oven until warmed through, about 10 minutes.