Lightly oil a cutting board to prevent sticking. Dip 2 sheets of rice paper (3 sheets if you like the noodles thicker) in lukewarm water, stack them evenly, and place them on the oiled board. Brush the top layer with more oil to keep it moist and prevent from sticking together. Cut the stack into 1-inch thick noodles or your desired size. As you peel the noodles from the cutting board, immediately transfer the noodles to a bowl of lukewarm water to keep the noodles moist and separated.
Heat oil in a pot until hot but not smoking. In a heatproof bowl, add chili flakes, garlic, green onion, sesame seeds, and sugar, then pour the hot oil over the mixture to sizzle. Add soy sauce, water or broth, and salt, stirring to combine. Set the sauce aside.
Drain the noodles then immediately transfer to the sauce bowl and toss well to coat.
Garnish the noodles with fresh cilantro and serve immediately for the best texture and flavor.