Slice the cucumber into matchsticks or half moons and toss together with the rice vinegar, salt, chopped cilantro, and green parts of the sliced green onion. Cover and set aside.
Bring a pot of water to a boil for the noodles.
Heat a pan over medium-high heat with cooking spray. Once hot, add the ground beef and cook for 2-3 minutes until a crust forms on one side. Then break the beef apart with a spatula and fully cook.
While the beef cooks, mix together the beef sauce ingredients. Add the sauce to the fully cooked beef and cook until the sauce thickens, about 2-3 minutes.
Cook the noodles once you add the sauce to the beef. Cook for 4 minutes, reserve about 1 cup of water, and drain the rest.
Add the cooked noodles back to the pot with the sauce packets from the noodles, tahini, and ¼ to ½ cup of the reserved cooking water as needed. Stir until smooth and creamy.
Plate the noodles and top with the ground beef and cucumber salad. Garnish with toasted sesame seeds and crunchy chili onion or chili oil, if desired.