Make quinoa as directed on package, using water and salt. Remove from heat; stir in lemon peel and lemon juice. Cover to keep warm.
Meanwhile, cook garden vegetable medley as directed on bag.
In 10-inch skillet, melt butter over medium heat. Add bell pepper and onion. Cook 3 to 5 minutes, stirring frequently, until vegetables are crisp-tender. Stir in cooked garden vegetable medley. Spoon quinoa mixture onto serving platter; top with vegetable mixture.