To make the Vietnamese Caramel BBQ Sauce: To a saucepan add the 2 tablespoons water and sugar. Over medium heat simmer until it turns a deep golden brown, about 5 minutes. Watch carefully.
In a small bowl mix together 2 tablespoons water, fish sauce and lime juice; carefully add (it will sputter) to the carmelized sugar mixture, heating low until the caramel dissolves.
Add the chili, garlic and shallots and simmer to reduce by half, about 3-5 minutes.
Mix the cornstarch into the remaining 1 tablespoon water, add it into the sauce and simmer until it thickens, about a minute. Remove from heat and set aside.
For the Burgers: With a light hand, thorougly mix the pork, garlic, ginger, green onion, cilantro, fish sauce, 1 tablespoon of the prepared Vietnamese Caramel BBQ Sauce, lime zest and jalapeno and salt, if desired. Form the mixture into 4 patties.
Grill over medium heat until cooked, about 4-6 minutes per side. Assemble burgers by layering the pork patty on a bun, topped by the pickled veggies, cucumber, jalapeno, cilantro and bun top spread with mayonnaise.