Heat water to boiling in a large saucepan.
Stir the rolled oats into the water. Turn off the heat and let the oats and water sit while you mix the other ingredients together. This will soften the oats.
Preheat oven to 350 degrees and spray 9x13 pan with cooking spray. I used a glass Pyrex baking dish which is safe under the broiler at 450 degrees if it is 2 " from the heat source and the broiler is preheated. If in doubt use a metal baking pan.
Place the brown sugar, granulated sugar and butter into a large mixing bowl and cream them together with a mixer.
Add the eggs and vanilla extract and mix well.
Place flour, soda, cinnamon and salt together in a large mixing bowl and whisk together.
Mix 1/2 of rolled oats and flour mixture into the creamed mixture and mix together.
Add other 1/2 of rolled oats and flour mixture to batter and mix until everything is combined.
Pour batter into prepared 9x13 pan and bake for about 35 minutes or until toothpick inserted into center of cake comes out clean.
While the cake is baking make the topping.
Melt butter, sugar and milk or half and half together in a large saucepan over medium heat. Stir in the vanilla, pecans and coconut. Remove from the heat.
When cake is done spread the topping mixture over the top of the cake and place it under the broiler for 2-4 minutes. Watch it closely and take it out when coconut is browned. Be careful it doesn't burn.
Let the cake cool for about 15-20 minutes. It's great served warm but develops more flavor as it sits.