Heat the oil in a large stockpot over medium heat until shimmering. Add shallots & jalapeño and sauté until soft, about 5 minutes.
Stir in garlic, ginger, lemongrass, & chili powder. Sauté until deeply fragrant, about 2 minutes.
Add broth & coconut milk and bring to a simmer. Stir in peanut butter & chili oil until incorporated, then let simmer for 10 minutes.
While broth simmers, soak the rice noodles according to package directions.
Reduce the heat to low and add shrimp. Cook until shrimp are just barely cooked, about 5 minutes, then turn heat off.
Stir sesame oil, lime juice, & salt into the broth.
Fill bowls halfway with rice noodles, then fill with broth & shrimp. Top with cilantro leaves & black sesame seeds & enjoy!