In a medium bowl, combine canned tuna, diced jalapeños, shredded sharp cheddar cheese, mayonnaise, and mustard. Mix thoroughly until well incorporated.

If meal prepping, transfer the filling to an airtight container and refrigerate for up to 3 days.

Lay out bread slices on a clean surface and spread a generous amount of the tuna filling on each slice.

Top each slice with additional shredded cheese and jalapeño slices if desired.

Preheat your oven to 400°F (200°C). Place the assembled melts on a baking sheet and bake for 7-9 minutes.

For an extra crispy topping, broil for the last 2-3 minutes.

Remove from the oven, let cool for a minute, then slice in half and serve warm.