In a non-stick pan over medium heat, cook the sausage on both sides until no longer pink in the middle or to an internal temperature of 155°F using a thermometer.
Heat the oil in a non-stick pan over medium heat. Crack the eggs into the pan and cook until the whites start to become firm (break the yolks if desired). Flip the eggs over, add the cheese, and cook for 1 minute longer.
Lightly toast the croissants.
Portion the eggs on the croissant with the sausage, serve with blueberries.