Here is the full list of all 35 I am Bread achievements.
Get an A++ on a Zero Gravity level
Finish a Story level with less than 1% edibility
Use more than one heat source to toast yourself in a single Story run
Complete all Cheese Hunt levels
Finish a Story level with 100% edibility without using the Magic Marmalade
Finish a Story level with both sides covered in butter
Stand upright on the skateboard and ride it for 1 meter as the Wholemeal bread
Get an A++ on all Rampage levels
Complete all Zero Gravity levels
Finish a Zero Gravity level using less than 100 fuel
Get an A++ on all Bagel Race levels
Climb atop the Garbage Truck on Story mode
Complete all Rampage levels
Spill the salt
Get an A++ on a Story level
Take out the Starch Destroyer
Get an A++ on a Rampage level
Complete all Bagel Race levels
Get an A++ on a Bagel Race level
Complete all Story levels
Stay airborne for over 5 seconds on any mode except Zero Gravity
Finish a Story level with both sides covered in jam
Finish a Story level using Magic Marmalade
Become inedible
Get an A++ on a Cheese Hunt level
Get an A++ on all Story levels
Get an A++ on all Cheese Hunt levels
Get an A++ on all Zero Gravity levels
Finish a Cheese Hunt level with 100% integrity