Heat the oil in a non-stick frying pan and cook the garlic for 1 minute. Tip in the tomatoes with 2 tbsp of water and cook for 5 minutes until the skins of the tomatoes start to split. Stir in the harissa, yogurt and some seasoning, and keep warm.
Meanwhile, cook the spaghetti following pack instructions, then drain well, reserving a little of the pasta water. Tip the spaghetti into the sauce, add 1-2 tbsp of the cooking water and toss.
Add the lemon juice, tear in the basil and divide between 2 plates.