In a bowl, whisk the eggs with salt, black pepper, and red pepper (if using).
Melt the butter in a skillet over medium heat. Add chopped spring onions and diced tomato, sautéing for 2–3 minutes until softened.
Pour the egg mixture into the skillet, stirring gently until scrambled and cooked through. Remove from heat.
Place the tortilla on a clean surface. Sprinkle half of the mozzarella cheese over one side, then top with scrambled eggs, spinach, and the remaining cheese.
Fold the tortilla in half and return it to the skillet over medium-low heat. Cook for 2–3 minutes per side until golden brown and the cheese is melted.
Slice in half and serve warm.