Preheat oven to 350º F.
Lightly grease a muffin tin.
Crack all of the eggs into a large bowl and whisk until eggs are cohesive. Add the salt, pepper, half of the scallions and 1/4 cup of the grated cheddar cheese. Give the mixture a good stir and carefully pour it into each of the muffin cups on the muffin tin, about 3/4 of the way up.
Top each of the servings with the rest of the scallions, cheese, and evenly distribute the chopped sardines over each one.
Bake in the oven for 20 minutes, or until the eggs are cooked through.
Let the egg muffins cool for about 10 minutes before trying to pop them out of the muffin tin. Use a knife along the edges of each egg muffin to help release it from the muffin tin if needed.
Serve the muffins on their own or on toasted English muffins with a slice of cheese and other additions of your liking.