Drain yogurt for 1 hour in a cheesecloth-lined strainer to remove some of its water. In a bowl, combine the yogurt, garlic and 1/2 teaspoon salt. Sprinkle the remaining 1/2 teaspoon salt over the grated cucumber and drain, 10 to15 minutes, to extract excess water. Add drained cucumber to yogurt, along with pepper, and mix well. Cover and refrigerate until chilled, about 1 hour. Drizzle with olive oil and garnish with mint leaves. Serve with pita triangles or grilled fish.