2) Meanwhile, peel the prawns, reserving the shells. Devein the prawns and refrigerate.
3) Heat one tablespoon of the oil in a soup pot over a medium heat; add the prawn shells and tomato puree, and cook, stirring, until the shells turn pink, about three minutes. Add the ham hocks, halved garlic, thyme, lemon zest and 3.5L cold water. Bring to a boil, then reduce the heat to maintain a simmer. Cook, uncovered, until the meat falls off the ham hock, about 1 1/2 hours.
4) Strain the broth into a bowl (you should have about 1.5L broth), and save the ham hocks. When the ham hocks are cool enough to handle, pull the meat from the bone; discard the rind, fat and bone. (This can be done a day ahead.)
5) In a large soup pot, heat the remaining two tablespoons of oil over a medium heat. Add the onion, sliced garlic and half the jalapeno. Crush the tomatoes through your hands and add to the pot, along with their juices, and cook until the onions soften and the tomatoes dry, about ten minutes.
6) Add the stock, ham and black-eyed peas and bring to the boil. Adjust the heat to maintain a simmer, and cook, uncovered, until the peas soften, but hold their shape, about 20 minutes.
7) Add the escarole and the remaining jalapeno and cook until the greens wilt, about seven minutes. Stir in the prawns and 1 1/2 teaspoons of salt and cook until the prawns turn pink and curl, about three minutes. Divide the soup evenly into warmed bowls. Serve with a lemon wedge.