In a food processor, finely chop the garlic, basil and cashews with the nutritional yeast and lemon juice. With the machine running, gradually drizzle in the oil and blend until slightly grainy or creamy, to taste. Using a spatula, scrape down the sides of the food processor as needed. Season lightly with salt and pepper. The pesto will keep in an airtight container for 1 week in the refrigerator or 6 months in the freezer. Cover the surface of the pesto with a thin layer of oil to prevent it from oxidizing.