Preheat the oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
In a large mixing bowl, combine the flour, sugar, baking powder, baking soda, salt, and cocoa powder. Mix well.
Add the milk, vegetable oil, eggs, and vanilla extract to the dry ingredients. Beat on medium speed for 2 minutes until well combined.
Stir in the boiling water until the batter is smooth (the batter will be thin). Pour the batter into the prepared baking pan.
Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Allow the cake to cool in the pan for 10 minutes.
Using the handle of a wooden spoon, poke holes all over the top of the cake.
In a small bowl, mix the sweetened condensed milk with the shredded coconut and chopped pecans. Pour this mixture over the cake, ensuring it fills the holes.
Let the cake cool completely, then spread the chocolate frosting evenly over the top.
Serve at room temperature or chilled.