Making Feta Grilled Cheese Sandwich with Spinach is simple when you follow these easy steps:

1. Preheat a skillet or non-stick frying pan over medium heat.
2. In a small bowl, combine feta cheese, spinach, salt, and pepper. Mix until well combined.
3. Spread softened butter on one side of each slice of bread.
4. Place two slices, buttered side down, onto the preheated skillet.
5. Evenly distribute the feta and spinach mixture on top of the bread in the skillet.
6. Optional: Layer sliced tomatoes or roasted red peppers for added flavor.
7. Top with the remaining slices of bread, buttered side up.
8. Cook until the bread is golden brown and toasted, about 3-4 minutes.
9. Carefully flip the sandwiches and cook the other side until golden and the cheese is melted, another 3-4 minutes.
10. Remove from the skillet and let sit for a minute before slicing in half.

These straightforward steps will guide you through creating this incredible sandwich with ease!