In a large saucepan or skillet, heat olive oil over medium heat.
Add the diced onion and cook until it becomes translucent, 2-5 minutes. Add the minced garlic and sauté for an additional 30 seconds until fragrant, being careful not to burn it.
Pour the tomatoes, salt, pepper and Italian seasoning into the pan.
Reduce the heat to low and let the sauce simmer uncovered for about 20 minutes, stirring occasionally. This allows the flavors to meld and the sauce to thicken.
Serve immediately over pasta, as a pizza base, or with your favorite dish. Store leftovers in an airtight container in the refrigerator for up to 5 days, or freeze for up to 3 months.