Heat the vegetable oil in a large skillet over moderately high heat.

Add the thinly sliced yellow onion and cook, stirring occasionally, until it begins to soften (about 3 minutes).

Add the sliced serrano chile and cook for 1 minute.

Add the store-bought green curry paste and 1/2 cup of the coconut milk and bring to a simmer, stirring until the curry paste has completely dissolved.

Add the rest of the coconut milk and bring to a simmer.

Add the trimmed and cut green beans and simmer, stirring occasionally, until they are bright green (3 to 4 minutes).

Add the zucchini matchsticks and thinly sliced chicken breasts and simmer until the chicken is cooked through and the zucchini is crisp-tender (5 to 8 minutes).

Stir in the fish sauce and freshly squeezed lime juice.

Serve the chicken garnished with chopped fresh basil leaves, with steamed white rice and lime wedges on the side.