Bring a 6-quart saucepan of water to a boil. Place 3 half-pint canning jars along with their bands and lids in the boiling water. After about 30 seconds, remove the lids from the water with tongs and transfer to a kitchen towel on the counter. After about 10 minutes, use tongs to transfer the jars and bands to the kitchen towel and let air-dry.
In a food processor, pulse garlic until finely chopped. Add walnuts and pine nuts to the food processor and pulse until finely chopped. Add oregano and pulse a few more times until just combined.
Heat 1⁄4 cup of the olive oil in a 12" skillet over medium-high heat. Stir in the walnut-pine nut mixture, raisins, salt, and black pepper, to taste. Cook, stirring occasionally, until the nuts are lightly toasted, about 5 minutes. (The pine nuts will toast faster than the walnuts, so take care not to burn them.) Remove the skillet from the heat and let cool slightly.
When the jars are dry but still hot, distribute the nut-and-raisin mixture evenly between the jars, tightly packing each one, leaving about 1" of space below each rim. Pour about 4 tbsp. extra-virgin olive oil into each jar so that it seeps to the bottom and covers sauce by 1⁄2". Wipe the rims of the jars with a hot damp towel. Cover and seal each jar with a lid and screw the bands on tightly.
The foriana sauce will keep in the refrigerator for up to 9 days. If using less than a full jar's worth of sauce in a preparation, top off the remaining sauce with a little more extra-virgin olive oil to cover by 1⁄2".