Marinated Feta Turkey Sandwich

Whisk together olive oil, vinegar, chiles, black pepper, coriander, and salt in a medium bowl. Thinly slice one onion half into rings; reserve remaining onion half for another use. Scatter about half of the onion rings over bottom of a 9- x 13-inch baking dish; pour half (about 2/3 cup) of olive oil mixture over top. Arrange feta slabs in an even layer over onions. Scatter remaining onion rings over feta, and top with remaining olive oil mixture. Cover and chill in the refrigerator for at least 2 hours, flipping feta after 1 hour.

Place focaccia, cut sides up, on a work surface. Spoon about 3 tablespoons feta marinade evenly over each bread half. Arrange feta and onion slices evenly on bottom half of bread; top with tomato, cucumbers, turkey (if using), and microgreens. Drizzle additional marinade (1 to 2 tablespoons) over microgreens; sandwich with top bread half. Cut into quarters, and serve.