Prepare canner, jars, and lids.

Pour pureed tomato sauce into large saucepan. Stir in lemon juice, oregano, pepper, salt and garlic powder. Boil hard, stirring frequently, until mixture is the consistency of a thin commercial sauce, about 15 minutes. Remove from heat.

Ladle hot sauce into hot jars, leaving 1/2 inch (1 cm) headspace. Remove air bubbles and adjust headspace, if necessary, by adding hot sauce. Wipe rim. Center lid on jar. Screw band down until resistance is met, then increase to fingertip-tight.

Place jars in canner, ensuring they are completely covered with water. Bring to a boil and process 1/2 pints and pints 35 minutes. Remove canner lid. Let sit 5 minutes, remove jars from water, cool, label, and store.