Step 1: In a bowl, combine the tuna, spring onions, chilli, lemon juice, lemon zest, mayonnaise and Sriracha. Season with salt and black pepper and mix well.
Step 2: Butter one side of each slice of bread.
Step 3: Heat a frying pan over a medium-low heat. Place two slices of bread butter-side down into the pan.
Step 4: Top each with a slice of Mexicana Cheese, followed by the tuna mixture, then another slice of cheese.
Step 5: Finish with the remaining bread, butter-side facing up. Press down gently with a spatula.
Step 6: Cook for 3–4 minutes per side, turning carefully until golden and crisp, with the cheese fully melted.
Step 7: Slice in half and serve immediately while hot and gooey.