In a large sauce pan, toss the diced onion with the olive oil and salt. Saute over medium heat until the onion is just transparent.

Add the garlic, zucchini, and mushrooms, saute until just softened. Add the diced tomatoes, basil, oregano, thyme, and pepper, saute for about five minutes more.

Add the crushed tomatoes, bring to a boil, then lower the heat and simmer for at least one hour, stirring occasionally. Add the tomato paste and let cook for ten minutes more. Serve over hot pasta.