Loaded Summer Squash Casserole

Name: Loaded Summer Squash Casserole
Ingredients: 1 tablespoon extra-virgin olive oil; 4 medium yellow squash , sliced into ¼-inch-thick rounds (about 8 cups ); 1 tablespoon unsalted butter; 1½ tablespoons all-purpose flour; ¾ cup whole milk; 2 tablespoons reduced-fat sour cream; 1½ cups shredded sharp Cheddar cheese , divided; 1 teaspoon salt-free garlic-and-herb seasoning blend; ¼ teaspoon smoked paprika; ¼ teaspoon salt; ¼ teaspoon ground pepper; 1 large egg , beaten; ½ cup finely crumbled cooked bacon (about 3 slices ), divided; 1 medium scallion , thinly sliced