Make the stir fry sauce: In a medium bowl, whisk together the water, soy sauce, honey, rice vinegar, sesame oil, garlic, ginger, cornstarch, and red pepper flakes, if using.

Make the stir fry. Heat the olive oil in a large skillet or wok over high heat. Add the red and yellow peppers, mushrooms, broccoli, snap peas, and carrots and toss. Cook, stirring occasionally, for 3 to 4 minutes, or until the vegetables soften slightly.

Reduce the heat to medium and pour in the stir fry sauce. Stir and cook for 1 to 2 minutes, or until the sauce thickens and the vegetables are crisp-tender. Season to taste. Top with the green onions and sesame seeds and serve.