Quickly dampen the friselle by passing them under running water. In a small bowl, mix 2 Tbsp water, 1 Tbsp vinegar, a drizzle of olive oil, and a pinch of salt. Sprinkle this mixture over the friselle arranged on a serving plate and let them soften.
Cut the cherry tomatoes in half and season them in a bowl with olive oil, salt, and fresh oregano leaves. Let them marinate until ready to use.
Check that the broccoli rabe doesn't have thick stems that need removing, then break it into pieces and cook for 10 minutes in plenty of boiling salted water. Drain and season while still warm with olive oil and salt in a bowl. Let cool to room temperature.
Top the softened friselle with the broccoli rabe, cherry tomatoes, and large flakes of Rio Mare tuna. Drizzle with the tomato marinade and serve.
Note: If friselle isn't available, substitute with thick slices of rustic bread, lightly toasted and brushed with the water-vinegar mixture.