Corn and Zucchini Quesadillas

olive oil

onion, coarsely chopped

Salt

garlic cloves, minced

medium zucchini (about 1 pound), halved lengthwise and thinly sliced crosswise

frozen corn kernels (4 ounces)

chopped fresh cilantro (optional)

flour tortillas (8-inch)

grated Pepper Jack cheese