Preheat oven to 350°F (175°C). Grease a 9×13-inch baking pan and set aside.

1. Combine oats and boiling water in a bowl. Let sit for 15–20 minutes to soften and cool slightly.
2. In a large bowl, cream butter, granulated sugar, and brown sugar until light and fluffy.
3. Beat in eggs and vanilla extract until well combined.
4. Stir in the soaked oats.
5. In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.
6. Gradually mix dry ingredients into the wet mixture until just combined.
7. Pour batter into prepared pan and smooth the top.
8. Bake for 35–40 minutes, or until a toothpick inserted in the center comes out clean.
9. Optional topping: While the cake bakes, combine butter, brown sugar, milk, coconut, and pecans in a saucepan. Heat until bubbling, then stir in vanilla extract.
10. Spread topping over hot cake immediately after baking.
11. Broil for 1–2 minutes until topping is golden and bubbly. Watch carefully to avoid burning.
12. Let cool slightly before serving.