Cook the rice noodles according to package instructions. Drain and set aside.
In a large pot, heat the vegetable oil over medium heat. Add the sliced onion and sauté until translucent, about 3-4 minutes.
Stir in the minced garlic and ginger, cooking for an additional minute until fragrant.
Add the red curry paste to the pot, stirring well to combine with the onion mixture.
Pour in the beef broth and coconut milk, bringing the mixture to a simmer.
Stir in the soy sauce, peanut butter, lime juice, and brown sugar. Season with salt and pepper to taste.
Add the sliced beef to the pot and cook for about 5-7 minutes, or until the beef is cooked through.
Divide the cooked rice noodles among serving bowls and ladle the hot soup over the noodles.
Garnish with fresh cilantro and serve with lime wedges on the side.