Start by heating 2 tbsp. of the reserved tuna oil in a large pan and fry the onion and garlic for 4 minutes or until soft. Add in three drained tuna, mix together well then add in the fresh spinach leaves and cook for 2 minutes to wilt. Remove off the heat, allow to cool down then palace into a large mixing bowl. Add in the sliced peppers, artichoke hearts, olives, capers, beans, mint and crumbled feta. Season well with black pepper (avoid using salt as many ingredients are salty) and mix together well. Roll out the puff pastry block on a floured work surface to a large rectangle 40cm x 30cm in size and trim off any uneven edges. Spread the red pesto down the middle, ⅓ of the width from side to side. Place the filling on top like a sausage, leaving ⅓ of pastry on both sides. Cut the pastry into strips from the filling outwards, leaving still attached. Brush the pastry lightly with the beaten egg and start to overlap the pastry strips over the fillings, enclosing it in from top to bottom. Place onto a lined baking tray, brush all over with beaten egg and sprinkle over the seeds. Bake in the oven at 200°C for 30-40 minutes or until golden brown and cooked through. Allow to rest for 5 minutes before serving cut into thick slices.