For the chicken sausage: If raw, cook in a 400°F oven to an internal temperature of 160°F using a thermometer. If already cooked: Preheat a non-stick pan over medium heat and brown the chicken sausage slices on each side.
Lightly toast the croissants.
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 or until the cheese is melted.
Portion the eggs on the croissant with the sliced sausage, serve with grapes.