01 - Mash the avocado in a small mixing bowl. Stir in mayonnaise, Greek yogurt, chives, basil, parsley, and lemon juice. Season with salt and pepper as desired.
02 - Spread an even layer of softened butter on one side of each bread slice.
03 - Arrange two slices of bread, buttered side facing down, on a clean surface. Top each with a slice of provolone or mozzarella, half of the prepared spread, spinach, cucumber, green onions, a slice of cheddar, and another slice of provolone or mozzarella.
04 - Place the remaining bread slices on top, buttered side up, to form two full sandwiches.
05 - Warm a large skillet or griddle over medium-low heat.
06 - Transfer the sandwiches to the skillet. Cook for 3 to 4 minutes per side, pressing gently, until the bread turns golden and the cheese melts.
07 - Remove from the skillet, let rest briefly (about 1 minute), slice, and serve warm.