Cut bacon crosswise into 1-inch pieces. Cook in skillet over medium heat until crisp; remove to absorbent paper. Reserve 3 tablespoons drippings. Return 1 tablespoon drippings to skillet; add onion and cook until transparent.

Spread rice in an 11 3/4 × 7 1/2-inch baking dish; top with half the bacon and onion. Combine flour and remaining 2 tablespoons drippings in saucepan; mix well. Gradually add milk and cook over medium heat until thickened and bubbly, stirring constantly. Stir in salt, pepper and Parmesan cheese. Pour 1 cup sauce over bacon and rice. Top with zucchini and olives. Sprinkle with remaining bacon; pour remaining sauce over top. Cover tightly with aluminum foil and refrigerate overnight.

Remove from refrigerator and let stand at room temperature for 15 minutes. Bake at 375ºF for 25 minutes. Remove the foil, and continue to bake for 20 minutes.