Preheat oven to 350 degrees Fahrenheit.

In a small bowl, whisk together flour, cornstarch, and baking soda.

Set the dry ingredients aside.

In a large bowl, cream together brown sugar, white sugar, and margarine until smooth and creamy.

Add egg and vanilla extract to the creamed mixture.

Mix until well combined.

Gradually blend the dry flour mixture into the wet creamed mixture.

Mix until just combined.

Fold in chocolate chips, sweetened coconut, and chopped walnuts.

Mix until evenly distributed.

Using a tablespoon sized cookie scoop, portion out 12 balls of dough.

Place the dough balls onto greased parchment paper-lined cookie sheets.

Bake in the preheated oven for 10 to 12 minutes.

Check the cookies after 10 minutes to ensure they are not burning.

Adjust baking time as needed, baking until lightly browned.

Remove from oven and let cool on baking sheet for a few minutes before transferring to a wire rack to cool completely.