Spread about 1 tablespoon of Pesto onto each slice of bread.
On one slice of bread, add 1 slice of cheese, sliced avocado, crumbled goat cheese, spinach, second slice of cheese, then top it with second slice of bread. Press together gently.
Heat 1 tablespoon olive oil in a frying pan over medium low heat. (If you want to use butter, add it to the oil and let it melt). Add the sandwich to the oil and cook until bread is golden brown. Press down on the sandwich lightly, then flip the sandwich over and cook until second side is golden brown.