Preheat oven to 350 degrees F. Line rimmed baking sheets with parchment paper.
In a large bowl using an electric mixer, cream together 1/2 cup softened butter, 1/2 cup granulated sugar, and 1/2 cup packed brown sugar until light and fluffy, 2 to 3 minutes. Beat in 1 large egg and 1 teaspoon vanilla, scraping down the bowl as needed.
Add in 1 cup flour, 1/2 teaspoon baking soda, and a 1/4 teaspoon each baking powder and salt, and beat until combined. Finally add in 1 cup quick-cooking oats, 1 cup Rice Krispies, and 1/2 cup sweet shredded coconut. Mix until thoroughly incorporated.
Using a cookie scoop, form balls of dough (about 2 tablespoons of dough each.) Roll them in the palm of your hands so they're smooth.
Place on prepared baking sheets about 2 inches apart.
Bake in the preheated oven for about 10 to 11 minutes, until lightly golden around the edges.
Remove from the oven and let cool for a couple minutes on the baking sheets, then transfer to a cooling rack to cool completely. (They will firm up as they cool, but you still want a chewy center.)