Rice vermicelli are translucent Chinese noodles cooked simply by soaking in hot water. Coiled nests of these noodles can be found at Asian markets and large supermarkets. If your frozen veggie mixture doesnt include peas, edamame is a nice addition to this soup.
Break rice noodles into bits, and place in large bowl; cover with boiling water, and set aside.
Pulse tempeh and white parts of onions in food processor several times, until coarsely chopped.
Heat peanut oil in large pot over medium-high heat. Add tempeh mixture, and sauté 3 minutes, or until lightly browned, stirring frequently. Add 4 cups boiling water, and scrape up any browned bits sticking to bottom of pot.
Add frozen vegetables and edamame, if using. Reduce heat to medium, cover, and cook 7 minutes, or until vegetables are tender. Remove from heat.
Drain noodles, and add to soup. Stir miso into 1/2 cup hot water, then add to soup. Stir in onion leaves and sesame oil. Add tamari to taste, and serve.