Heat olive oil in a soup pot. Saute onions, garlic and ginger over medium heat until soft onions are soft. Add the stock, nori, wakame and mushrooms. Bring to a boil and reduce heat to simmer, cooking about 10 minutes. Remove from heat and add rice noodles. Let noodles soften in the hot water for 5 to 10 minutes. Ladle into bowls and add a splash of soy sauce or seasoned rice wine vinegar to taste.