Peel the chayote, slice it in half and then, slice each half into half again. Using a mandoline, thinly slice each piece of chayote.
Place a steaming basket into a pot and add 1 inch of water. Cover and bring to a boil over high heat. Once the water starts boiling, toss the grated chayote into the pot.
Lower the heat to medium and steam the chayote for about 10-15 minutes until fork tender.
While the chayote is cooking, thinly slice the onion and transfer to a bowl. Add the extra virgin olive oil, apple cider vinegar, salt, and mix well.
Once the chayote is ready, mix it with the onions mixture. Refrigerate for 1 hour before serving chilled.
Sprinkle some chopped scallions on top to add a pop of color to your summer salad.