Preheat oven to 350 degrees.
Then grease the sides and bottom of an 8 x 8 baking pan. You can also line the pan with parchment paper.
Combine oats, flour, coconut, nuts, sugar, baking powder, and melted butter in a medium-sized bowl.
Then stir to form a crumbly mixture.
Pat half of the mixture into the bottom of the prepared pan.
In a separate bowl, whisk sweetened condensed milk and lemon juice. Stir until combined.
Then pour the lemon mixture on top of the crust that is already in the baking pan.
Sprinkle the remaining crumb mixture on top.
Then bake for 40 - 45 minutes or until lightly brown.
Remove the pan from the oven and allow to cool completely before cutting into 9 squares.