1. Preheat oven to 450°.
2. Heat a Dutch oven over medium-high heat. Add 1 1/2 teaspoons oil; swirl. Add onion; sauté 4 minutes. Add garlic; sauté 1 minute, stirring constantly. Add sausage, salt, and pepper; sauté 5 minutes, stirring to crumble. Remove mixture from pan; drain. Wipe pan.
3. Return sausage mixture to pan. Stir in flour; sauté 30 seconds, stirring constantly. Combine milk and eggs, stirring well. Reduce heat to medium. Stir milk mixture into sausage mixture; bring to a boil, and cook 2 minutes, stirring constantly. Remove from heat; stir in spinach. Spoon spinach mixture into an 11 x 7-inch glass or ceramic baking dish coated with cooking spray.
4. Place bread in a food processor, and pulse until 1 cup coarse crumbs form. Heat a large skillet over medium-high heat. Add remaining 1 1/2 tablespoons olive oil to pan, and swirl to coat. Stir in crumbs, and sauté for 3 minutes or until toasted, stirring frequently. Sprinkle crumbs over spinach mixture, and top with cheese. Bake at 450° for 12 minutes or until bubbly.