Preheat the oven to 200 degrees F to keep the first batch of burgers warm.
For the burgers: Coat a large saute pan with olive oil. Add the onions, season with salt and bring to a medium-high heat. Cook the onions until they are soft and very aromatic, 7 to 8 minutes. Add the garlic and cook for 1 to 2 minutes. Turn off the heat and let cool.
In a large mixing bowl, combine the turkey, soy sauce, sambal oelek, ginger, water chestnuts, cilantro and the cooked onions and garlic. (Reserve the onion pan to cook the burgers in later.) Add one-quarter to one-half cup water; this will help the burgers stay nice and moist. Using your hands, squish everything together until they are really well combined.
Make and cook a little tester patty to be sure that the turkey is really well seasoned. Re-season if needed. If the burger is missing salt add more soy or just give a little sprinkey dink of salt.
When the burger mix is seasoned appropriately, form the mix into 4 equal size patties.
Coat the saute pan with new olive oil and bring to a medium-high heat. Place the burgers in the pan. Be sure not to crowd the pan, if you need to work in batches go ahead! Cook the burgers for 5 to 6 minutes on each side. Place the cheese, if using, on the burger and cook for 1 more minute.
Toast the buns in a broiler or toaster. Schmear each side of the bun lightly with the sambaal mayo. Put a burger on each of the bottom buns and top each burger with tomato, onion and lettuce. Close up each burger, give each one a little squish and eat em' up!
Beverage Pairing Suggestion: Light Lager