While the water is heating, dice the onion, grate or chop the garlic, and chop the tomatoes (if not using a can).
Add the pasta when the water is boiling (add salt and a small amount of oil for taste).
Heat oil in a large pot over medium heat, add the onion and garlic, cook for 5 minutes or until translucent.
Add the tomatoes. Note: if you use fresh tomatoes, the sauce will get a little runny. Only if you let it stand for a day will you get this creamy texture we're looking for.
Add the spinach.
Add the oregano, basil, red pepper flakes, salt, and pepper.
Add the tomato paste and the greek yogurt. Stir until both are dissolved into the sauce.
Now add the hard cheese.
Drain and add the pasta. Lower the heat to a simmer.
Stir occasionally for 1 minute. Taste and adjust the salt and pepper as needed.
Dinner is ready!