Combine ginger, coconut milk, milk, rice, sugar, and salt in a large saucepan. Scrape in seeds from vanilla beans; add pods. Bring to a boil, stirring occasionally. Reduce heat, cover, and simmer until rice is al dente, 15-18 minutes. Uncover and cook, stirring often, until rice is tender and mixture coats spoon, 5-8 minutes longer. Transfer to a large bowl and cover with plastic wrap, pressing directly onto surface. Let cool. Remove ginger and vanilla pods. Do ahead: Rice pudding can be made 2 days ahead; chill. Bring to room temperature before serving. Toast amaranth with chia and sesame seeds in a dry medium skillet over medium heat until they begin to pop and sesame is golden, about 3 minutes. Transfer to a small bowl; stir in cookies, raw sugar, and cinnamon Serve rice pudding topped with toasted seed mixture, mango, and a few mint leaves.