Preheat the oven to 350°F (175°C).
Grease a 12-cup muffin pan or line it with silicone baking cups.
In a small saucepan, melt 1½ tablespoons butter or ghee over low heat.
Whisk in the hot sauce, coconut aminos, and cayenne pepper until smooth. Remove from heat.
Heat the remaining ½ tablespoon butter or ghee in a skillet over medium-high heat.
Sauté the diced bell pepper and green onions for about 5 minutes, until slightly softened.
Turn off the heat and stir in the spinach, cooked chicken, and prepared buffalo sauce.
Mix until everything is evenly coated.
Divide the chicken and vegetable mixture evenly among the muffin cups.
In a large bowl, whisk together the eggs, salt, and black pepper.
Pour the egg mixture evenly over the filling in each muffin cup.
Bake the Buffalo Chicken Egg Muffins for 18–20 minutes or until the eggs are fully set and a toothpick inserted in the center comes out clean.
Allow to cool for a few minutes before removing from the pan.
Serve warm or store for later meal prep.