Heat oil in a large saucepan over medium heat. Add the onion, the garlic, 1/2 teaspoon salt, and 1/4 teaspoon pepper, and cook until softened, about 5 minutes.
Add the tomatoes with their juice and thyme; simmer, stirring occasionally, until the sauce has thickened, 20 to 25 minutes. Sauce can be frozen for up to 2 months.