In a medium mixing bowl, combine the drained wild-caught tuna with clean mayonnaise, finely chopped onions, kosher salt, black pepper, paprika, and freshly squeezed lemon juice. Mix until well combined.

Rinse two English cucumbers under cool water and slice them into ¼-inch thick rounds. Lay half of the cucumber slices flat on a clean plate.

Spoon a generous dollop of the prepared tuna mixture onto each cucumber slice, spreading it evenly.

Gently place the remaining cucumber slices on top to create cucumber tuna sandwiches.

Insert toothpicks through the center of each stacked cucumber sandwich for easy serving.

Enjoy immediately or refrigerate assembled sandwiches for up to 3 hours.