Preheat the oven to 350°F (180°C). Lightly oil each opening of a 12-capacity muffin tin.
In a large bowl, whisk eggs. Then, add garlic, salt, red pepper flakes, salsa, and whisk until well incorporated.
Fill each muffin tin opening with chopped spinach, peppers, and sausage.
Pour the egg mixture to fill each muffin tin opening. Be sure to leave ¼ inch space at the top as the egg muffins will expand while they cook. Add in the cheese.
Bake the egg muffins for 15-20 minutes, or until set.
Let the egg muffins cool for 2 minutes before removing them from the muffin pan.
Top with a dollop of salsa and enjoy!