HEAT 4 tablespoons of the oil in a large saucepan over a medium heat and cook the onion and carrot for 10 minutes, stirring occasionally. ADD the garlic, oregano and rosemary and cook for 2 minutes. STIR in the flour and cook for 1 minute. REMOVE from the heat and stir in the tomatoes, stock, tomato paste, salt and pepper. RETURN to a high heat and bring to a boil, stirring regularly, then cover with a lid and reduce the heat to medium and cook for 10 minutes. ADD the lentils and cook, covered, for a further 10 minutes. WHILE the sauce is simmering, bring a large pot of lightly salted water to a boil and cook the pasta according to package directions. STIR the tuna and reserved tablespoon of olive oil into the sauce. DRAIN the cooked pasta into a colander and put the sauce in the bottom of the pot. TOP with the hot pasta and toss together gently to combine. SERVE with grated Parmesan cheese on top.