Preheat the oven to 350ºF and line a standard muffin tin with 12 baking cups. (I use these silicone liners for best stick prevention.)
Make sure your maple syrup and eggs are at room temperature. You can place the eggs in a bowl of warm tap water for a few minutes to help warm them up quickly. This will ensure that your muffin batter will be runny, like traditional muffin batter, and will easily mix and pour into the muffin cups. (Otherwise the coconut oil may harden and won't mix evenly into the batter.) In a large bowl, combine the coconut flour, maple syrup, coconut oil, lemon juice and zest, salt, baking soda, eggs, and vanilla, and use a whisk to stir the batter until smooth. The whisk should help break up any clumps, making the batter very smooth. Stir in the poppy seeds, then divide the batter evenly among the 12 baking cups.
Bake at 350ºF until the centers are firm to the touch and the edges are lightly golden, about 22 to 25 minutes. Cool completely before topping with the icing below.
To prepare the Creamy Lemon Icing, stir together the cashew butter, maple syrup, and lemon juice in a small bowl until smooth. Add water 1 teaspoon at a time, as needed to thin the icing to your liking. Drizzle it over the top of each muffin just before serving.
Leftover muffins can be stored in an airtight container in the fridge for up to a week.