Place the lentils, tomatoes and artichokes (with the liquid from the tins), 1/8 teaspoon cayenne pepper and the water into a large saucepan. Bring to a boil. Reduce heat to low and simmer until lentils are tender, about 20 minutes.
Meanwhile, bring a large saucepan of lightly salted water and 1 tablespoon of the olive oil to a boil. Add spaghetti and cook for 8 to 10 minutes or until al dente; drain. Return pasta to saucepan and cover to keep warm.
Heat remaining 2 tablespoons olive oil in a small frypan over medium heat and cook spring onions for about 3 minutes. Add 1/8 teaspoon cayenne and sesame seeds then cook until the seeds are lightly browned, about 2 minutes. Set aside.
Add the lentil mixture to the saucepan of pasta and toss to distribute evenly. Add the spring onion mixture then toss lightly again. Season with salt and pepper to taste.