1. Preheat oven to 375°.
2. Combine pork, turkey, and next 10 ingredients (through eggs) in a bowl; gently mix just until combined. Transfer mixture to a 9 x 5-inch loaf pan coated with cooking spray.
3. Bake at 375° for 55 minutes or until a thermometer registers 165°. Cool to room temperature; cover and refrigerate overnight.
4. Remove from pan. Cut scrapple into 10 slices.
5. Heat a large nonstick skillet over medium-high heat. Add oil to pan; swirl to coat. Add scrapple slices to pan; sauté 1 to 2 minutes on each side or until browned.
6. Place 2 scrapple slices on each of 5 plates. Top each serving with ketchup and horseradish, if desired. Serve warm.