On a cutting board, smash the prawns then coarsely chop. Place the prawns in a mortar and pestle with 1/2 the fresh dill, garlic, salt, and pepper. Dip the base of the pestle in the fish sauce and pound the mixture until minced, dipping the pestle in the fish sauce frequently while pounding, about 2 minutes. Take a teaspoon of the mixture and carefully stuff each pumpkin flower.
Coat each flower with egg white, then dust each flower lightly with the potato starch until dry and shake the excess starch off.
In a deep heavy-bottomed saucepan or wok add the vegetable oil and bring to 350 degrees F. Fry the dusted flowers in 3 batches until the flowers are crisp, not allowing them to go brown, about 1 1/2 minutes. Transfer the fried flowers to an absorbent paper towel to drain the excess oil.
Place the stuffed flowers on a long platter and garnish with the remaining fresh dill.
Serve as a shared entree with a squeeze of lime.
Hold a wooden chopstick in the hot oil as if measuring the depth. If the oil bubbles around the chopstick, the oil is hot enough to add the stuffed pumpkin flowers.