Preheat oven to 250F.
Combine cream cheese, mayonnaise, garlic powder and dill weed in a bowl; mix until smooth.
Fry bacon till crisp, remove and drain on paper towel.
Add onion to drippings and Sauté until tender.
Add bacon, onion, spinach and cheddar cheese to the cream cheese mixture; mix well.
Cut off top of bread and scoop out a cavity.
Spoon dip into bread and put the top back on.
Wrap the loaf in a double layer of foil and place on baking sheet. Bake in oven for 1 1/2 hours.