For the shrimp and pork filling: In a cast iron pan, heat the vegetable oil over medium heat. Place the pork in the pan and saute until brown and caramelized. Once the pork has browned, add the shallots, garlic, and chiles, cook for 1 to 2 minutes. Add the cumin and smoked paprika and stir. Add the shrimp and stir. Once the shrimp has turned pink, add the water chestnuts and stir. Add the sugar, cilantro stems, lime zest and juice, remove from heat. For the tomato salsa: Put the tomatoes and green onions in a small bowl. Add the lime juice, cilantro leaves and stems and mix. Season the salsa with sugar and salt. For the creamed avocado: Put the avocados in a bowl, add the lime juice and chopped green onion. Add the sugar and sour cream. Mash until the mixture is incorporated. Season with salt. To assemble the shrimp and pork tacos: Place the tortilla shells on a plate. Divide the pork and shrimp filling among the tortilla shells. Spoon the filling in the center of the taco. Spoon the creamed avocado and tomato salsa over the tortilla shells. Garnish with cilantro.