Combine flour, baking powder, and salt in a large bowl. Cut in the butter using a dough blade, forks, or your fingers just until the texture becomes coarse. Mix in the coconut milk just enough to bring together the dough. Add a little more coconut milk if too crumbly or a little flour if too sticky. Do not knead or overwork.
Preheat oven to 375˚F. Line two baking sheets with parchment or lightly grease.
Divide the dough into 5 equal pieces. On a lightly floured surface, roll a piece of dough into a thin circle about 8 inches wide. Fill the center with the cooled pineapple filling, leaving a border around the edges. Be careful not to overfill or you won't be able to close the pies or they may burst while baking.
Lightly wet the edges of the circle with a finger dipped in water. Fold the circle over the filling to make a half moon, pressing along the edges to seal. Use a fork, dampened with water to prevent sticking, to press down along the edges and pierce a few times over the top to create vents. Repeat with remaining dough and filling.
Arrange the pies on the prepared baking sheets, keeping them an inch apart. Bake in preheated oven until golden, about 35 minutes. Rotate the pans halfway through baking. Remove and allow to cool before serving, either as whole pies or cut into thick strips. If desired, you can sprinkle them with a little powdered sugar.