Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt.

In a separate bowl, beat the eggs until frothy, then add the buttermilk, melted butter, and vanilla extract. Mix until well combined.

Gently fold the wet ingredients into the bowl of dry ingredients using a spatula. Mix until just combined; be cautious not to overmix.

Carefully fold the grated zucchini and poppy seeds into the batter until evenly distributed.

In a small bowl, beat the cream cheese until smooth and creamy. Add powdered sugar and lemon juice, mixing until well blended.

Spoon the muffin batter into each lined cup, filling them about halfway. Drop a spoonful of the cream cheese mixture into the center of each muffin.

Place the muffin tin in the preheated oven and bake for 18-22 minutes, or until a toothpick comes out clean from the center of the muffins.

Once baked, allow the muffins to cool in the pan for about 5 minutes before transferring them to a wire rack.