"Passata" isn't available in your area, either? No worries, you can either make my homemade sauce as mentioned above (recipe link provided), or just make my basic "quickie recipe" that I use in a pinch when my summer sauces are all gone: 1 1/2 cups tomato puree* (12 oz.), 1 tsp. dried oregano, 1/2 tsp. dried Italian seasoning, 1/4 tsp. garlic salt, 1/4 tsp. sugar, 1/8 tsp. coarse ground black pepper, 1/8 tsp. garlic powder. (Adjust all to own taste.) This is the amount that you would need for this recipe. Double if you like a lot of sauce, making 4 chicken breasts, and would like to add some sauce to your cooked pasta as I did.
*For tomato puree, I just use canned whole tomatoes and run them through the food processor or blender with the juice.
Add all to a small saucepan and simmer until cooked down a little to desired thickness. Keep in mind that the sauce will further thicken during baking time.