In a Large pot bring water to a boil on high heat, adding a generous amount of salt. Add the pasta, stirring occasionally so as not to stick and cook 2 minutes less than package instructions. Reserve 1 cup of cooking water.
In the meantime, in a large, deep saucepan over medium heat add 2 tablespoons of the oil, wait a minute to heat and add the shrimps. Season with ½ teaspoon of salt and ½ teaspoon of pepper and cook for about 2 minutes each side. Remove from the pan and keep aside.
In the same saucepan add the remaining oil, heat for a minute and add the onions and the garlic. Sauté for 4 minutes until translucent and add the chili flakes sauteing for another minute until fragrant. Remove and discard the garlic and stir in the tomato paste and cook for a further minute.
Add the tomatoes along with 150 ml of water and cook for 10 minutes, add the spinach take off the heat and let wilt for 2 minutes. Add the yoghurt, parmesan cheese, half of the basil, the nutmeg, remaining salt and pepper and stir to combine.
Turn on the heat to low, strain the pasta and return to the pan along with the shrimps and toss for a minute. If sauce is too thick add from the reserved pasta water.
Remove from heat and serve garnishing with the remaining basil.