Preheat the oven to 375°F. In a medium bowl, whisk together flour, poppy seeds, baking powder, baking soda, and salt until well combined.
In a separate large bowl, add sugar and lemon zest together. Use your hands and mix the lemon zest and sugar together. Be sure to use your fingers to press the sugar and zest together. This will release more of the lemon oil from the zest making a more pronounced lemon flavor.
After the lemon zest and sugar are well mixed, add the whole milk, eggs, melted and slightly cooled butter, avocado oil, and vanilla extract. Whisk together until combined. The butter may appear to re-harden as you mix, that’s okay.
Add dry ingredients to wet ingredients and stir together until just combined.
Add lemon juice. Stir until just until the lemon juice is fully incorporated. It’s okay to see some lumps.
If using liners, arrange paper liners in the muffin pan. Fill muffin cups about three-quarters of the way.
Let the batter rest in the muffin pan for 5-10 minutes (resting the batter is not mandatory but you will get a better rise). Bake for 12-18 minutes or until a toothpick comes out clean or with loose crumbs (not wet batter) when inserted in the center of a muffin. For a slightly crunchy crust, let the edges brown slightly.
Once they are done, let the muffins cool for 3-5 minutes before transferring onto a cooling rack