Place frozen bananas, vanilla extract, and a splash of milk in a food processor and blend on high. Add more milk, if needed and scrap down the sides as you go. The bananas will become creamy and thick like soft serve ice cream. Once combined, add the blue spirulina and blend once more until blue throughout.
Pour nice cream into 3-4 bowls, top with cookie dough, then place 2 candy eyes in each bowl on top of the cookie dough. Serve immediately!