Melt butter in a large skillet over medium heat; cook and stir yam and onion in the melted butter until lightly browned, 5 to 10 minutes. Mix zucchini, yellow squash, red bell pepper, green bell pepper, oregano, basil, salt, and black pepper into the yam mixture; cook and stir until vegetables are heated through and partially tender, 5 to 10 minutes.
Transfer vegetable mixture to a casserole dish; sprinkle vegetables with Cheddar cheese and bread crumbs. Spray top of casserole with butter-flavored cooking spray.
Bake in the preheated oven until topping is browned and cheese is melted, about 25 minutes.