Prepare lasagna. (If using frozen lasagna, cook according to package instructions). This recipe works great using leftover lasagna.
In a small bowl, combine softened butter, minced garlic, and paprika until well mixed.
Spread each slice of bread with the garlic butter mixture. On two of the slices, buttered side down, sprinkle on some of the shredded mozzarella cheese. Onto each slice, layer a small square portion of the prepared lasagna, then top with more shredded cheese and the second slice of bread, buttered side up.
Note: Taller stacks of lasagna tend to be slippery. For a more manageable sandwich, you can use 1-2 layered lasagna noodles instead.
Cook the sandwiches in batches on a hot skillet or griddle over medium heat, until golden brown and crispy on both sides and warmed through, about 3-4 minutes.
Cut each sandwich into quarters, using toothpicks to hold together. Garnish with chopped parsley and serve.