Drain pineapple; reserving juice; set juice aside.
Place half of the pineapple slices in an ungreased 5-quart slow slower.
Top with ham.
Mix together reserved pineapple juice, orange marmalade, brown sugar and red pepper flakes.
Spoon marmalade mixture over ham. Top ham with remaining pineapple slices.
Cover and cook on low for 5 to 6 hours or until heated through.
Cut ham if needed, for cover to fit on crock pot.
Remove ham to platter, with two forks, shred ham.
Return to slow cooker and cook an additional hour on high.
Spoon ham on buns or rolls and serve with pineapple slices.