Preheat the oven to 350 degrees. Grease an 8-1/2-inch by 4-inch loaf pan with non-stick cooking spray and line with parchment paper.

In a medium bowl, combine the flour, baking powder and salt. In a large bowl, rub the grapefruit zest into the granulated sugar until it is very fragrant.

Use an electric mixer on high speed to beat in the eggs, oil and vanilla until pale and thick, about 4 minutes. On low speed, add half the dry ingredients followed by the Greek yogurt and 5 tablespoons grapefruit juice. Fold in the remaining dry ingredients and poppy seeds. Transfer the batter to the prepared baking pan, smoothing into an even layer.

Bake the loaf until golden brown and a toothpick inserted into the center comes out clean, about 50-60 minutes. Poke the top of the loaf and brush with 3 tablespoons grapefruit juice. Cool in the pan for 15 minutes and then transfer the loaf to a wire rack to cool completely.

In a small bowl, whisk together the confectioners’ sugar with 1 tablespoon grapefruit juice. Drizzle the icing over the loaf and sprinkle with poppy seeds. Let the icing set for 30 minutes before serving.

Store in an airtight container.