Cook the Fettuccine: In a large stockpot, bring water to a boil. Add 1 tablespoon of olive oil and the fettuccine. Cook according to package instructions, then drain (reserving 1 cup of pasta water) and set aside.
Prepare the Yogurt Mixture: In a small bowl, combine the Greek yogurt and sour cream. Stir together until smooth and set aside.
Sauté the Garlic and Tomatoes: While the pasta is cooking, heat the remaining tablespoon of olive oil in a large skillet over medium-high heat. Once hot, add the minced garlic and sun-dried tomatoes. Sauté for about 2 minutes until fragrant.
Make the Sauce: Reduce the heat to medium-low and stir in the diced tomatoes, tomato paste, and granulated sugar. Stir until well combined.
Incorporate the Creamy Mixture: Slowly whisk in the Greek yogurt and sour cream mixture. Whisk quickly to fully incorporate it into the sauce. Increase the heat to medium-high and let the sauce simmer for 5-7 minutes to thicken.
Finish the Sauce: Season the sauce with salt and pepper to taste. Add the grated parmesan cheese and baby spinach, stirring until the spinach wilts.
Combine with Pasta: Add the cooked pasta to the sauce and toss to coat. If the sauce is too thick, slowly add the reserved pasta water until you reach your desired consistency.
Serve: Optionally, top with crushed red pepper flakes for a bit of heat. Serve warm and enjoy!