Preheat oven to 350°F.

Dice tomatoes, onion, and zucchini. Pour into a 9x13 baking dish. Drizzle olive oil over the top, and sprinkle on basil, salt, and pepper.

Roast for about two hours, until tomatoes have broken down.

Let cool and puree in a blender or food processor. Taste and adjust seasoning.

Package into individual freezer-safe containers.