Prepare quinoa according to package directions.
Meanwhile, pulse mushrooms in a food processor, in batches if needed, until coarsely ground.
Heat oil in a large saucepan set over high heat; cook mushrooms, onion, garlic, poblano pepper, salt and pepper for 8 to 10 minutes or until slightly softened and starting to brown. Stir in walnuts and chili powder; cook for 3 to 5 minutes or until slightly softened.
Stir in tomatoes, lentils and broth; bring to boil. Cover and cook for 15 to 20 minutes or until flavors are blended. Stir in quinoa; cook for 2 to 3 minutes or until heated through. Garnish with cilantro.
For a kid-friendly chili, mash lentils before adding to soup for a smooth texture. Substitute beans if your child prefers the taste.