Transfer the plum tomatoes, juice and all, into a large mixing bowl. With bare clean hands, crush them into chunks so you're left with somewhat of a chunky tomato sauce.
Add the olive oil. With a microplane, grate the garlic to a paste and add it to the tomatoes. If you don't have a microplane, simply mince the garlic really well.
Finely chop the oregano and add it to the sauce.
Finally, add the salt and chili flakes, and gently stir the sauce to combine. Set it aside as you make your pizza. If you're not using it shortly after it's made, place it in a jar with a lid and refrigerate it. This good stuff will keep in the fridge for up to a week! You can also store it in an airtight container and freeze it for up to two months.