Preheat your oven to 375°F and line a muffin tin with 4 large paper liners, or lightly grease 4 muffin cups with cooking spray. In a medium mixing bowl, whisk together the flour, poppy seeds, baking powder, baking soda, and salt until evenly combined. Set that aside.

In a separate bowl, whisk the egg and honey together until smooth, then add the Greek yogurt, fresh lemon juice, lemon zest, melted coconut oil, and vanilla extract. Stir everything until it's nicely combined and uniform in texture.

Pour the wet ingredients into the dry ingredients and fold gently with a spatula until just combined. A few small lumps are totally fine — you do not want to overmix here or your muffins will turn out dense and tough. Stop mixing as soon as you no longer see dry flour streaks.

Divide the batter evenly among the 4 prepared muffin cups. Each should be about ¾ full. Place the muffin tin in the center rack of your preheated oven and bake for 18–22 minutes, or until the tops are golden and a toothpick inserted into the center comes out clean.

Let the muffins cool in the pan for 5 minutes before transferring them to a wire rack. If you're adding the glaze, mix together the powdered sugar and lemon juice until smooth, then drizzle it over the muffins once they've cooled completely. Enjoy!