Preheat oven at 375 degrees. Lightly spray rectangular baking tin with cooking spray.
Remove inner bread from centre of each slice of Baguette.
In a skillet, on medium to high heat, add oil, pancetta, sauté until crisp, remove from heat. Leave in pancetta oil. Using the same pan add onions, sauté until translucent, add garlic sauté until fragrant, add spinach sauté until wilted.
In a bowl, add Spinach mixture, crisp pancetta, mozzarella cheese, Italian seasoning, salt, and pepper, mix well until combined.
In a rectangular baking tin (8), add in each cavity, slice of butter, baguette slice, fill the centre with spinach mixture, then pour beaten egg on top, spreading egg evenly in each cavity.
Place in oven, and bake for 15 minutes, until golden brown and egg has cooked. Remove from heat and ready to serve.