Pour the boiling water over the noodles; set aside.
Heat the oil in a large wok or skillet over medium-high heat. Cook and stir the onion, zucchini, and mushrooms until softened; remove from skillet, reserving the oil, and set aside.
Reheat the remaining oil in the skillet. Cook and stir the chicken in the hot oil until no longer pink, about 5 minutes. Return the vegetable mixture to the skillet and add the fish sauce, curry paste, and sugar; stir to coat the chicken and vegetables with sauce.
Drain the rice noodles and add to the mixture.
Pour the coconut milk into the skillet and stir to combine.