Whisk broth, soy sauce, hoisin, oyster sauce, brown sugar, garlic, ginger, sesame oil, sriracha, and rice vinegar.
Place chicken in the slow cooker and pour the sauce over it.
Cover and cook on Low for about 3 hours, until the chicken shreds easily.
Stir cornstarch with water to make a slurry. Remove chicken and shred with two forks.
Whisk the slurry into the cooker. Switch to High and simmer 15 minutes to thicken.
Return shredded chicken to the thickened sauce and stir to coat.
Boil noodles in salted water until just shy of al dente. Drain well.
Add carrots, bell pepper, and mushrooms to the slow cooker. Cover 8–10 minutes until crisp-tender.
Fold in snow peas and most green onions for 2–3 minutes.
Toss in noodles until coated. Top with remaining green onions and serve hot.