To unlock these Secret Levels, you need to achieve an Expert Score in all of the levels of a restaurant. After doing so, a new tab labled "Expert Levels" will appear on the Restaurant Select Screen in Story Mode.

Level	How to unlock
Amour Amuck!	Complete Romantic Rendezvous with all Expet Scores
Harvest Hardcore	Complete Hometown Harvest with all Expert Scores
Homecooked Hunting	Complete Crypt Café with all Expet Scores
Snowed Under!	Complete Winter Wonderland with all Expert Scores
Water Park Madness!	Complete Coral Cave Café with all Expert Scores