Combine first 5 ingredients in a small bowl.
Heat 1/2 teaspoon oil in a 12-inch cast-iron skillet over high heat. Add half of zucchini slices; cook 2 minutes on each side or until browned. Remove zucchini from skillet; keep warm. Repeat procedure with 1/2 teaspoon oil and remaining zucchini slices. Serve with yogurt mixture.