Preheat a grill to high heat. Toss the zucchini lightly with olive oil and pinches of salt and pepper. Grill cut side-down for 2 minutes, then flip and grill skin-side down for 3 to 4 minutes or until char marks form. Remove from the grill, transfer to a plate, and squeeze with lemon juice.

In a small bowl, mix together the yogurt, lemon zest, garlic, and 1/4 teaspoon salt. Spread the yogurt on a medium serving platter, top with the zucchini, feta, mint, and red pepper flakes. Season to taste and serve.