Preheat your oven to 375°F and line a baking sheet with parchment paper.
Spread softened butter on one side of each bread slice and place butter-side up on the baking sheet. Toast in the oven for 5-7 minutes until golden and crispy.
Remove bread from oven and spread mayonnaise on each slice. Layer with spinach, turkey slices, tomato, and a dollop of cranberry sauce on each piece.
Top each sandwich with a slice of provolone cheese and return to the oven for 5-8 minutes until the cheese is melted and bubbly.
Season with salt and pepper, then serve immediately while hot and the cheese is still gooey.