Arrange bread on a baking sheet; coat with cooking spray. Bake at 375° for 10 minutes or until toasted, stirring once after 5 minutes. Combine 3 tablespoons water and squash in a medium microwave-safe bowl. Cover and microwave at HIGH 5 minutes or until tender. Drain. Combine bread cubes and squash in a large bowl.
Place 4 (8-ounce) ramekins on a baking sheet. Coat with cooking spray. Combine milk and next 7 ingredients (through eggs) in a bowl, stirring with a whisk. Add milk mixture to squash mixture, stirring to combine. Divide squash mixture among prepared dishes; top with cheese. Bake at 375° for 20 minutes or until stratas are puffed around the edges and a knife inserted in the center comes out clean, rotating the pan once after 10 minutes.