Place the rice noodles in a bowl. 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. Sprinkle with cilantro to serve.
