1.Toast quinoa in a dry skillet over medium heat, stirring often, until it becomes aromatic and begins to crackle, about 5 minutes. Transfer to a fine sieve and rinse thoroughly.
Meanwhile, bring broth to a boil in a medium saucepan over high heat. Add the quinoa and return to a boil. Cover, reduce heat to a simmer and cook gently for 8 minutes. Remove the lid and, without disturbing the quinoa, add edamame. Cover and continue to cook until the edamame and quinoa are tender, 7 to 8 minutes longer. Drain any remaining water, if necessary.
Whisk lemon zest and juice, oil, tarragon and salt in a large bowl. Add peppers and the quinoa mixture. Toss to combine. Divide among 4 plates and top with walnuts.