Prepare the crab by cutting away the face (this can taste bitter), slicing just behind the eyes. Next, lift the flap on the underside of the crab and cut this off. Loosen the top "shell" of the body and remove the gills. Rinse the crabs well.
For the marinade: Mix together the ginger, peanut oil, rice wine, five-spice powder and cayenne in a bowl. Add the crabs, cover with plastic wrap and marinate for 30 minutes.
Fill a wok halfway with peanut oil. Place over medium-high heat and heat the oil to 350 degrees F, or until a cube of bread turns golden brown in 15 seconds and floats to the surface.
In a shallow bowl, stir together 2 heaping tablespoons sweet potato starch with the beaten eggs (the batter can have some lumps). Remove the crabs from the marinade. Dip the crabs in the batter and then dredge again in the remaining sweet potato starch. Carefully lower the crabs into the hot oil using a slotted spoon. Deep-fry until golden brown, 3 to 4 minutes. Drain on paper towels and season with the salt and dried chile flakes while they are still hot.
Serve immediately over Mango Noodle Salad and garnish with the chives and Fresno chiles.
Mango Noodle Salad:
In a large bowl, toss together the noodles, spinach, chiles and mango and set aside.
Whisk together the vinegar, chili sauce, fish sauce, lime juice and peanut oil. Taste and adjust flavors if desired. Dress the salad just before serving.