Prepare quinoa as label directs. Makes about 1 cup.
In large skillet, heat oil over medium-high heat. Add mushrooms and taco seasoning; cook 5 minutes or until browned, stirring frequently. Add 1/2 cup water; cook 5 minutes or until liquid is absorbed, stirring occasionally. Transfer mushrooms to large bowl; stir in quinoa.
In same skillet, stir beans and 1/4 cup warm water; cover and cook over low heat 3 minutes or until heated through, stirring occasionally.
Place flour tortillas on work surface; spread with bean mixture. Place 1 crispy taco shell in center of each flour tortilla; press sides of flour tortilla to adhere with beans. Fill layered taco shells with mushroom mixture; top with cheese, lettuce, tomato and onion.
Serve tacos with taco sauce and sour cream, if desired.