Drain the tuna thoroughly in a sieve. That way the filling won't turn watery later.
Halve the avocado, remove the stone and put the flesh into a bowl. Mash lightly with a fork.
Add the tuna, mustard and lemon juice to the avocado. Mix everything and season to taste with salt and pepper.
Wash the cucumbers and halve them lengthways. Scoop out the soft centre with a teaspoon to make room for the filling.
Spoon the avocado and tuna mixture evenly into the cucumber halves.
Serve straight away so the cucumber stays crunchy and the avocado fresh.
Good to know
When things need to be quick, this is one of those meals that still looks like a proper lunch. Fresh, creamy and refreshingly simple.
Swaps
Mustard → Greek yoghurt (adds protein). Cucumber → romaine lettuce leaves (also crunchy). Lemon juice → lime juice (similarly fresh, with a slightly different aroma).
Allergens
Contains fish and, depending on the product, mustard as an allergen; suitable for children in small, well-mashed portions, and during pregnancy it's common with well-chilled, ready-to-eat tuna in moderate amounts. Contains: mustard.