Put the lentils in a saucepan and cover with cold water. Bring to a boil and simmer for about 30 minutes, or according to the package directions, until just tender. Drain well.

Meanwhile, heat the oil in a large saucepan. Add the onion, garlic, carrots, and celery. Cover and cook on low heat for 5 minutes. Stir in the tomatoes, stock,red bell pepper, tomatoe past, rosemary, and oregano. Cover and simmer for 20 minutes, until the sauce is thickened and the vegetables are tender. Add the lentils and cook, stirring, for an additional 5 minutes. Season with salt and pepper.

While the sauce is cooking, bring a large saucepan of lightly salted water to a boil. Add the spaghetti, bring back to a boil, and cook according to the package directions, until tender but still firm to the bite. Drain well, then divide the spaghetti among four warm bowls. Spoon the sauce over the pasta and sprinkle with the basil leaves. Sever immediately with the grated cheese on the side.