Heat a skillet over medium heat and add the olive oil.
In a bowl, mix the chopped spinach, cream cheese, feta cheese, sun-dried tomatoes, garlic powder, salt, and pepper until well combined.
Spread the spinach mixture evenly onto one slice of bread.
Top with mozzarella cheese and place the second slice of bread on top.
Place the sandwich in the heated skillet and grill for about 3-4 minutes on each side, or until the bread is golden brown and the cheese is melted.
Remove from the skillet and let it cool for a minute before slicing in half.