Cook bacon in a Dutch oven over medium heat until crisp. Add fennel and onion to pan; sauté 8 minutes or until soft. Remove bacon mixture from pan. Add undrained oysters to pan; cook 3 minutes or until edges of oysters begin to curl. Remove oysters from pan; discard cooking liquid. Chop oysters; add to bacon mixture. Stir in ham, parsley, and artichokes.
Combine ricotta, nutmeg, red pepper, and 1 egg in a bowl; stir with a whisk until well-blended. Add 4 eggs; stir well. Stir in milk and spinach.
Arrange half of toast in a single layer in a 13 x 9-inch baking dish coated with cooking spray. Spoon half of oyster mixture evenly over bread. Pour half of milk mixture over oyster mixture; repeat layers. Sprinkle with Parmesan and paprika. Cover; refrigerate 8 hours or overnight.
Preheat oven to 350°.
Uncover and bake at 350° for 45 minutes or until set.
Note: Fresh shucked oysters, which are often packaged in pop-top containers, come in three sizes; select, standard, and stewing. Standard are average size.