Microwave the udon noodles: In a large microwavable bowl, add the frozen udon noodles and add 1 cup of water. Microwave for 3 minutes or until the noodles are defrosted. Once defrosted, drain and set aside.
Prepare the sauce: In a small bowl, whisk together the water, rice vinegar, dark soy sauce, low sodium soy sauce, vegetarian oyster sauce, sesame oil and cornstarch until smooth. Set aside.
Cook the beef: Heat a large skillet or wok over medium-high heat. Add the ground beef and cook, breaking it apart with a spatula, until browned and cooked through, about 5-7 minutes. Drain any excess fat if necessary. Make sure the ground is crispy.
Sauté the aromatics: Add the minced garlic and the white parts of the green onions to the skillet with the beef. Stir-fry for 1-2 minutes until fragrant.
Cook the broccoli: Toss in the broccoli florets and stir-fry for another 3-4 minutes until they turn vibrant green but are still crisp-tender.
Combine everything: Lower the heat to medium, pour in the prepared sauce, and bring it to a simmer. Allow the sauce to thicken for 1-2 minutes, then add the cooked udon noodles, tossing everything together to coat the noodles evenly.
Finish and serve: Remove from heat, garnish with the green parts of the green onions, and chili crisp for heat.