Preheat the oven to 375 degrees.
Heat the oil in a nonstick pan on medium heat. Saute the mushrooms and thyme, until the mushrooms are soft and any liquid in the pan has completely evaporated. Remove from heat and set aside.
In a large bowl mix together the ground beef, worcestershire sauce, soy sauce, garlic powder, salt and pepper. Separate the beef into two equal portions. Separately form both portions into even elongated loafs. Using your fingers create a well in the center one loaf. Place the mushrooms and brie in the center and place the other loaf on top, using your hands to form and fuse both loafs together.
Place on a foil lined baking sheet and cook in the oven for 30 minutes or to an internal temperature of 150 degrees using a thermometer. Remove from the oven and let meatloaf sit 5 minutes before slicing into portions.
In a bowl, whisk the sugar and hot water until the sugar is dissolved. Whisk in the apricot preserves, soy sauce, and rice vinegar until the sauce is well-combined. Let the sauce sit for 5 minutes and mix again before serving.