To make the pork, put all the ingredients except the pork into a food processor and process to make a gooey paste.
(One teaspoon chopped Scotch bonnet or hot sauce makes a moderately fiery marinade; use more or less to taste.)
Rub the pork with the paste, wearing rubber gloves, as the pepper can burn.
Cover loosely and refrigerate for 1 day.
One hour before serving, wipe off the marinade with a towel.
Roast pork over a charcoal fire, turning regularly, for 35 to 50 minutes, or until the interior is 140 degrees.
Cool.
To make the soup, finely puree the tomatoes, melon, 2 cucumbers, salt, pepper, chili- pepper flakes and buttermilk in a blender or food processor, working in batches.
Transfer to a bowl and stir in the orange zest, mint and coriander.
Adjust the seasoning and chill.
Slice the remaining cucumber into i-inch half-moons and refrigerate.
Ladle the soup into 6 bowls.
Toss the diced pork with the cucumber half-moons and add to the bowl.