Spread butter evenly on one side of each slice of bread.
On the unbuttered side of two slices of bread, layer the feta cheese, mozzarella cheese, chopped olives, and sun-dried tomatoes.
Sprinkle dried oregano over the cheese mixture.
Top with the remaining two slices of bread, buttered side up.
Heat a non-stick skillet or griddle over medium heat.
Carefully place the sandwiches in the hot skillet. Grill for 4-5 minutes per side, or until the bread is golden brown and the cheese is melted and gooey.
Remove from skillet, let cool slightly, then slice in half and serve immediately.
Notes
Serve with a side salad or your favorite soup for a complete meal.