In a small saucepan, combine water, coconut sugar, tamarind paste, 1 clove of minced garlic, 2 bird's eye chilies, and 0.25 tsp sea salt.
Simmer the sauce over medium heat for 10 minutes until slightly thickened, then strain through a fine-mesh sieve and set aside.
In a large bowl, mix the ground chicken thigh, egg, 2 cloves of minced garlic, 0.5 tsp sea salt, and black pepper until well combined.
Gradually fold in the tapioca starch until a workable dough forms that is no longer sticky to the touch.
Shape the dough into small cylinders or discs using lightly floured hands to prevent sticking.
Bring a large pot of water to a boil and drop the dumplings in, cooking until they float to the surface.
Remove the dumplings with a slotted spoon and drain them well on a wire rack.
Heat avocado oil in a non-stick skillet over medium-high heat and sear the dumplings until the skin is golden and crispy on all sides.
Serve the warm empek-empek with the spicy vinegar sauce and fresh diced cucumber for a cooling crunch.