In a small pot, char the onion and ginger over medium-high heat for 2-3 minutes until slightly blackened and aromatic.
Add the chicken bone broth, star anise, and cinnamon stick to the pot and bring to a gentle simmer for 15 minutes to infuse the flavors.
While the broth simmers, cook the rice noodles in a separate pot of boiling water according to package directions, then drain and set aside.
Season the chicken breast with sea salt and black pepper, then poach it directly in the simmering broth for 8-10 minutes until fully cooked through.
Remove the chicken, slice it thinly against the grain, and strain the broth through a fine-mesh sieve to remove the onion, ginger, and whole spices.
Place the cooked noodles in a deep serving bowl, top with the sliced chicken, and pour the hot, strained broth over the top.
Finish the dish by garnishing with fresh bean sprouts, cilantro, Thai basil, and a squeeze of fresh lime juice.