Grease a crock cooker with olive oil.
In large bowl, mix squash, zucchini, onion and 1 tablespoon butter.
In the crock cooker, mix squash mixture, 1 cup of the bread crumbs, 1/2 cup of the cheese, the sour cream, garlic, salt and pepper and broth.
In small bowl, mix remaining 1 cup bread crumbs, remaining 1/2 cup cheese and the melted butter.
Sprinkle crumb mixture over squash.
Cover and cook on low heat setting for 2 hours. Uncover and let stand 30 minutes before serving.
Sprinkle with chopped scallions and serve warm.