Mix oats and coconut in a large bowl until thoroughly combined.
Stir sugar, cocoa powder, milk, and margarine together in a saucepan over medium heat until the mixture is smooth. Bring to a boil and cook for 2 minutes, stirring constantly. Pour over the oats and coconut and quickly mix to coat. Drop by tablespoon onto prepared baking sheet; let cookies cool and harden. Store in an airtight container.
