This versatile pesto can be tossed with pasta for a quick supper or spread on crostini for a sophisticated appetizer.
Place walnuts, bread and garlic in a food processor or blender; blend until smooth. Blend in spinach, yogurt, Parmesan and oil. Season with salt and pepper.
Tip: To toast walnuts: Spread nuts on a baking sheet and bake at 350°F, stirring once, until fragrant, 7 to 9 minutes.