Cook your noodles according to the package instructions.
In a medium-large pot, stir together the water, chicken, white/light green scallion pieces, ginger, soy sauce, maple syrup, and salt. If using fresh veggies, add them now. If using frozen veg or leafy greens (these cook much faster), add them towards the end of simmering.
Bring to a boil over high heat, then cover with a lid and reduce the heat to low or medium-low to maintain a simmer for 5 minutes.
Flip the chicken over and continue to simmer, covered, for about 5 more minutes or until the chicken is cooked through (time will vary a lot depending on thickness of the chicken).
Transfer the chicken to a cutting board to rest for 5 minutes, then chop or shred it up.
Meanwhile, transfer about 1 heaping cup of the broth to a medium bowl or liquid measuring cup. Add the tahini and whisk until totally smooth, adding more broth if needed. Stir back into the pot along with the chicken and lime juice.
Add the noodles to your bowl and ladle the soup over top. Top with scallions and sriracha or chili oil, if using.