Preheat oven to 325 F. Spray a 6-cup mini Bundt pan with baking spray.
Sift together flour, baking powder, baking soda & salt in a bowl.
In the bowl of a stand mixer, beat the pureed avocado & butter with the sugar until completely combined. Beat in egg. With the mixer on low speed, beat in lemon juice/milk mixture until just combined.
Add flour mixture in 3 additions, mixing each addition until just combined. Once the flour mixture is incorporated, increase speed to medium & beat for 20 seconds longer. Be careful to not overmix. Divide batter between the 6 mini cups.
Bake until a wooden pick inserted in center comes out clean, about 25 minutes. Cool cakes in pan on a rack for 10 minutes before inverting to cool completely.
Lemon Glaze
In a small bowl, combine enough fresh lemon juice with powdered sugar to make a glaze consistency. Drizzle over cooled cakes. Garnish with pepita seeds or pistachios & lemon zest.