Place rice noodles in a large bowl and cover with hot water (doesn't need to be boiling). Allow to soak for 20 minutes. Drain and rinse with cold water - the noodles will finish cooking in the sauce.
Heat the sesame oil in a pan over medium heat. Add the yellow onion and cook for 3 minutes, stirring frequently. Add the ginger, garlic and white pepper. Cook for an additional 30 seconds.
Add the sriracha, red curry paste, rice wine vinegar, soy sauce and broth to the pan. Bring the mixture to a boil and add the noodles. Lower heat and cook until the noodles absorb all of the liquid, stirring constantly.
Before serving, stir in the green onions & red pepper flakes (if using) and drizzle with sesame oil. Serve while hot.
Video
Notes
To make these less spicy: lessen or omit the sriracha, red pepper flakes and red curry paste.