Preheat the oven to 400 degrees. Lightly grease a large 12-well muffin pan. Melt the coconut oil and set it aside to cool. Combine the flour, sugar, baking powder, salt, baking soda, cinnamon, nutmeg and ginger in a bowl. Place the buttermilk, squash, egg and melted coconut oil in a second bowl and beat to blend ingredients thoroughly. Add the wet ingredients to the dry ones and mix just until combined. Fold in the raisins if used. Fill muffin wells evenly with the batter. Bake for 20-25 minutes or until a cake tester inserted into the center comes out clean. Let the muffins cool for 15 minutes. Remove the muffins from the pan and serve warm or let cool to room temperature.