Prepare a large baking sheet by lining it with parchment paper or a silicone baking mat.

In a medium saucepan over medium heat, melt the butter. Add the brown sugar and sweetened condensed milk. Stir continuously until the mixture begins to bubble—this should take about 3 minutes.

Remove the saucepan from the heat. Stir in the vanilla extract, salt, and ground cinnamon (if using), combining thoroughly.

Quickly fold in the shredded coconut and chopped pecans, mixing well until evenly distributed.

Add the quick oats and stir until the mixture is thick and everything is well coated.

Working quickly, drop heaping spoonfuls (about 2 tablespoons each) of the mixture onto the prepared baking sheet. Flatten or shape them slightly with the back of your spoon.

Allow the cookies to cool at room temperature for at least 20 minutes or place them in the refrigerator for faster setting.

Once firm, enjoy immediately or transfer to an airtight container for storage.