Place squash into a large pot and cover with water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 10 minutes. Drain and mash squash in a bowl.
Stir 1 cup corn flakes, margarine, eggs, sugar, seasoned salt, and black pepper into mashed squash. Transfer mixture to a 2-quart casserole dish. Sprinkle about 1/4 cup cornflake crumbs over squash mixture.
Bake in the preheated oven until bubbling and topping is lightly browned, 20 to 25 minutes.
Tips & Tricks
How to Make Stuffed Summer Squash
See how to make summer squash stuffed with sausage and goat cheese.
How to Make Green Bean Casserole
See how to make classic French onion and green bean casserole.