In a medium sized bowl, combine the cream cheese, butter, crab meat, diced onion, and salt
Place the sliced mozzarella on a parchment paper lined baking pan
Bake the mozzarella in a 375 F oven for about 5 minutes or until the slices are bubbly and browned on the edges
Remove the mozzarella from the oven and place about 1 TBS of filling on each slice. The amount will depend on the size of you mozzarella slices
Fold over the mozzarella to form a triangle and seal the edges
Place back into the oven for about 2 minutes or until the filling is heated
Remove from the oven and let cool slightly
Serve and enjoy!