Preheat the oven to 400 degrees F.
Line and Coat muffin tin with baking spray.
Combine the zest and sugar in a food processor; pulse until the zest is very finely chopped into the sugar.
Add buttermilk (or yogurt), oil (or butter), egg,1 tablespoon of lemon juice and vanilla into a bowl.
Pour buttermilk mix into the food processor and run until blended. Do not overmix!
Combine flour, baking powder, baking soda and salt in a large bowl.
Add the buttermilk mixture and fold until almost blended.
Stir in poppy seeds using a rubber spatula.
Divide the batter evenly among the muffin cups.
Bake until the edges and tops are golden, 20 to 25 minutes.
Let cool for 5 minutes.
While the muffins are cooling, place confectioner’s sugar in a medium bowl, then add 2 Tbsp fresh lemon juice and the vanilla extract. Whisk until smooth. (If icing is too thick to drizzle, add the last tablespoon of lemon juice and up to 1 tablespoon of milk, as needed, to reach desired consistency.)
Drizzle icing over slightly cooled muffins, then serve immediately.