Grilled Zucchini and Corn Tostadas

soft flour tortillas or corn tortillas (taco size)

small zucchini, cut in half lengthwise

ears sweet corn, husked

Olive oil, for brushing zucchini and corn

Salt and black pepper,

green onions, chopped

fresh cilantro, chopped

ripe avocados, pit removed and chopped

limes, cut into wedges

cotija cheese