In a pan, add tofu, mushrooms, oil, cook for 7-10 min stirring often, until starting to brown. Add dark soy sauce and 2 tbsp sauce. Stir, cook 1 min.
Put some water in small bowl. Have the filling mixture and wonton wrappers handy. Take 1 tbsp of tofu mixture, place in center of wonton wrapper. With finger, wet two adjacent edges of wonton square.
Fold over other two sides, press down firmly, squeezing out air. You should have a triangle. Fold in two sides of the triangle to overlap each other, secure with bit of water, press firmly.
Once all are folded, cook dumplings for 3 to 5 min (until wrapper is fully cooked) in steamer or large pan with some water in bottom and covered, as a makeshift steamer. Just be extremely careful when handling the dumplings, to avoid breaking them.
Remove to serving plate, brush with the sauce, top with garnish and serve with the rest of the sauce as a dipping sauce.