In a saucepan, cook the pearl barley in salted boiling water for approximately 25 minutes. Drain, rinse under cold water and transfer to a bowl.
Meanwhile, place the pine nuts in a cold frying pan and toast them over medium heat until lightly browned on the surface. Set aside.
Wash and prepare the tomatoes. Cut off the top, including the stem, to create a lid for each tomato. Carefully scoop out the pulp, leaving the tomatoes hollow to create small containers.
Cut the PICCOLO PESTO into small cubes and add them to the bowl with the pearl barley. Add the tuna, a few fresh basil leaves torn by hand, the toasted pine nuts and one-third of the tomato pulp.
Season all the ingredients with salt and black pepper to taste, then mix well.
Fill the hollowed tomatoes with the prepared mixture and place their lids back on top. Bake in a fan-assisted oven at a temperature not exceeding 160°C (320°F) for approximately 10 minutes, allowing the filling to warm through and the tomatoes to seal.

Serve the stuffed tomatoes garnished with a few ingredients that echo the flavours of the filling, together with a few additional cubes of PICCOLO PESTO.