Soak the dried mushrooms in water for 1 hour, then drain.
Cut the carrot, bell pepper, and mushrooms into strips; cut the onion into wedges; and chop the garlic and ginger into fine cubes.
Heat 3 tablespoons of oil in a wok or non-stick pan over medium-high heat. Fry the carrots, mushrooms, peppers, and onions for 5-7 minutes until tender-crisp. Add the ginger and garlic in the last minute of cooking. Pour in the broth, then add the soy sauce, sweet soy sauce, fish or oyster sauce, sambal oelek, and five-spice powder. Bring to a boil, season with salt to taste, and thicken with sauce thickener.
Mix the egg with water. Add flour, potato starch, salt, and baking powder; mix until smooth without lumps. Let the batter rest for 10 minutes, then add 5 tablespoons of oil and let stand for another 20 minutes.
Heat the oil for deep-frying in a saucepan to 170-180°C (338-356°F) over medium-high heat.
Cut the fish into bite-sized pieces, dust with flour, dip in the batter, and let excess drip off.
Fry the fish pieces for 2-3 minutes until light brown, then drain on paper towels and cool for 5 minutes. Return to the hot oil and fry for 1-2 minutes until golden brown.
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