In a large pot, heat the sesame oil over medium heat. Once hot, toss in the minced garlic and grated ginger and sauté until fragrant, about 1-2 minutes.

Pour in the chicken or vegetable broth and bring it to a simmer. Add the rice noodles and cook according to package instructions, usually around 3-5 minutes, until they're tender but still have a bit of bite.

Drop in the shrimp and sliced shiitake mushrooms. Cook for 2-3 minutes or until the shrimp turns pink and the mushrooms are tender.

Stir in the soy sauce and lime juice. Taste and add a pinch of chili flakes if desired.

Ladle the soup into bowls and top with chopped green onions and fresh cilantro. Squeeze additional lime for extra flavor if desired.