Rinse quinoa under cold water and drain. Combine quinoa and water (or chicken broth) in a saucepan, bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes or until the quinoa is tender and the liquid is absorbed. Fluff with a fork and set aside.
In a small bowl, whisk together soy sauce, honey, sriracha (if using), and cornstarch. Set aside.
Heat olive oil in a large skillet or wok over medium-high heat. Season chicken with salt and pepper and add it to the skillet. Cook, stirring occasionally, for 5-6 minutes, or until chicken is cooked through. Remove chicken from the skillet and set aside.
In the same skillet, add minced garlic and grated ginger, cook for 1 minute, or until fragrant. Add mixed vegetables and cook for 3-4 minutes, or until they are tender but still crisp.
Add the cooked chicken back to the skillet. Pour in the prepared sauce and cook, stirring constantly, for 2-3 minutes, or until the sauce has thickened.
Stir in the cooked quinoa and mix well. Serve hot, garnished with chopped green onions.