Layered Zucchini Corn Casserole

Butter, oil or nonstick cooking spray for baking dish

medium zucchini, ends trimmed, thinly sliced lengthwise (about 2 pounds)

butter

bunch scallions, white and light green part only, chopped (or 1 small onion, finely chopped)

jalapeno peppers, finely chopped (seeded if desired)

garlic, minced

cream cheese, softened

mayonnaise

whole milk or half-and-half

large eggs, beaten

salt

freshly ground black pepper (or to taste)

corn kernels, fresh or frozen (thawed if frozen)

shredded Monterey Jack cheese

butter crackers (such as Ritz or Townhouse), crushed