Heat a large skillet over medium-high heat. Add 1 pound 90% lean ground beef and 3 minced garlic cloves. Cook, breaking the beef into crumbles, until no longer pink, about 4–5 minutes. Transfer the beef to a plate and set aside.
Carefully drain any excess grease from the skillet. Return the skillet to medium-high heat and add 1 tablespoon olive oil.
Add 1 diced red bell pepper, 1 sliced zucchini, ½ cup sugar snap peas, ½ cup shredded carrots, and 8 ounces sliced mushrooms to the skillet. Sauté, stirring occasionally, until the vegetables are tender-crisp, about 3–4 minutes.
Return the cooked ground beef to the skillet and stir to combine with the vegetables.
In a small bowl, whisk ½ cup packed light brown sugar, ½ cup reduced-sodium soy sauce, 1 tablespoon sesame oil, ½ teaspoon ground ginger, ¼ teaspoon crushed red pepper flakes, and ½ teaspoon pepper until smooth.
Pour the sauce over the beef and vegetables. Bring to a simmer and cook, stirring, until the sauce is slightly thickened and coats the mixture, about 2–3 minutes.
Serve over 2 cups cooked white rice and top with sliced green onions and sesame seeds for garnish.