Cactus, Chayote, And Green-Apple Salad

Ingredients

• 1 lb fresh nopales (prickly pear cactus paddles; about 5; see cooks' note, below)
• 2 chayotes (1 pound total), peeled, halved lengthwise, and seeds discarded, then cut into 1/4-inch-thick sticks (3 to 4 inches long)
• 1 granny smith apple, left unpeeled, halved, cored, and thinly sliced lengthwise
• 2 scallions, trimmed and thinly sliced
• 4 navel oranges
• 3 tablespoons fresh lime juice
• 1/4 teaspoon salt
• 1/8 teaspoon black pepper
• 1/3 cup raw (green) hulled pumpkin seeds
• 5 tablespoons olive oil
• rounded 1/8 teaspoon cayenne