First, in a food processor, (not a Vita-Mix), place 3 1/2 cups of Watermelon and 1 cup of mango and blend until smooth.
Next, dice up the remaining 1 1/2 cups of Watermelon and 1 cup of mango into tiny pieces and add them to the puree. In a small separate bowl, combine the lime juice, mint, ginger, honey and cardamom. Add this to the previous mixture and stir well.
Now chill everything in the fridge and serve in a few hours.