Combine the soy sauce, hoisin sauce, sugar, rice vinegar and tahini in a bowl and mix well.
Cook the noodles according to package instructions.
In a large deep skillet on medium high heat, add sesame, vegetable oil and the ground beef. Sprinkle pepper and stir until brown, around 5 minutes.
Pour in the soy sauce mixture and bring to a simmer until the sauce coats the beef and begins to get crispy, another 4-7 minutes. Add baby spinach, cover, and cook for 3 minutes. Stir well.
Add the chili oil, stir, and remove from heat.
Toss in the noodles.
Garnish with chopped scallions.
