In a small bowl, whisk together soy sauce, water, Mirin, honey, cornstarch, grated garlic, grated ginger, sesame oil, and crushed red pepper flakes to prepare the stir fry sauce. Set aside.
Heat a large skillet over medium-high heat and add ground beef seasoned with salt and black pepper. Cook until browned and no pink remains, about 7-8 minutes, keeping beef in chunks.
Transfer cooked beef to a paper towel-lined plate using a slotted spoon to drain excess fat. Remove liquid fat from skillet without cleaning.
Add peanut oil to the same skillet over medium-high heat. Add broccoli, onion, red bell pepper, sugar snap peas, carrots, and mushrooms. Cook for 8-10 minutes until vegetables are tender yet crisp.
Return the cooked ground beef to the skillet along with the prepared sauce. Stir well to coat the beef and vegetables evenly. Cook for 45 seconds to 1 minute until sauce thickens.
Remove from heat and serve immediately. Sauce will continue to thicken as it cools.