Cook the pasta according to the package directions. Reserve 1 cup of water before draining.

Heat olive oil in a large skillet over medium-high heat. Add garlic and sundried tomatoes. Sauté a couple minutes, until fragrant. Reduce heat to medium, and add diced tomatoes and tomato paste. Stir until well combined. Mix in sugar.

In a small bowl combine Greek yogurt and sour cream. Whisk into tomato mixture. Increase heat to medium-high and let simmer for 5-7 minutes, it will start to thicken slightly.

Season with salt and pepper to taste, and add the crushed red pepper flakes. Mix in the baby spinach, it will take about a minute for the spinach to wilt. Once the spinach is wilted toss with the cooked pasta. Add water ¼ cup at a time, if necessary to get to your desired consistency.

Serve with Parmesan cheese if desired.