Lightly coat a 1 1/2-quart souffle dish or casserole* with cooking spray. Tear off an 18×12-inch piece of heavy foil; cut in half lengthwise. Fold each piece lengthwise into thirds. Crisscross the foil strips and place the dish in the center of the crisscross; set aside.
For filling, in a large bowl beat cream cheese, sugar, orange juice, flour, and vanilla with an electric mixer on medium speed until combined. Beat in sour cream until smooth. Beat in eggs with mixer on low speed just until combined. Stir in orange peel. Pour filling into prepared dish. Cover dish tightly with foil.
Pour warm water into a 3 1/2- to 5-quart slow cooker. Using the ends of the foil strips, transfer dish to cooker. Leave foil strips under dish.
Cover and cook on high-heat setting for 2 1/2 hours or until center is set. Using foil strips carefully remove dish from cooker; discard foil strips. Cool completely, uncovered, on a wire rack. Cover and chill for 4 to 24 hours before serving.
Garnish with orange slices and crystallized ginger if using.