01 - Combine turkey, cheddar cheese, mayonnaise, Dijon mustard, red bell pepper, spring onions, Cajun seasoning, smoked paprika, salt, and black pepper in a medium mixing bowl. Mix thoroughly to ensure even distribution.
02 - Arrange bread slices and spread softened butter on one side of each slice.
03 - Place four bread slices, buttered-side down, on a clean surface. Evenly distribute turkey-cheddar mixture over each, spreading to the edges.
04 - Cover each filled slice with another bread slice, buttered-side up.
05 - Preheat a large skillet or sandwich press over medium heat. Cook assembled sandwiches in batches if needed for 3 to 4 minutes per side, gently pressing, until golden and cheese is fully melted.
06 - Remove sandwiches from skillet, slice as desired, and serve immediately while hot.