Here is the full list of all 32 Hell Pie achievements.
Smash Nugget against the wall
Meet Cupid
Meet Chef
Collect your first ingredient
Complete the Sprint Horns challenge level
Complete the Ram Horns challenge level
Complete the Light Horns challenge level
Complete the Arm Horns challenge level
Complete the Wing Horns Challenge Level
Defeat the boss of the Sewers
Defeat Gluttony
Defeat the Hell Pie
Trigger whale explosion
Plug in all Wi-Fi sticks
Use private insurance
Unlock Nugget Fart
Bring all sexy plants together
All Munchers freed
Complete dining room side quest
Monty Python did it with style, don't know how it's done here
Collect everything
Collect all Candymeat
Collect all Lucky Cats
Collect all Unilambs
Buy your first outfit
Get all outfits
Collect 1000 crystals
Collect 5000 crystals
Collect 10000 crystals
Witness a dark ritual
Destroy the crosses in Heaven
Hit 10 humans in the factory