White Pesto Pasta

Name: White Pesto Pasta
Prep time: 5 min
Cook time: 15 min
Total time: 20 min
Cuisine: Italian
Ingredients: 3/4 cup walnuts; 2 tsp fresh oregano (finely chopped ); 1 clove garlic (finely chopped or grated); 1 lemon (zest); 1 cup fresh ricotta; 2 oz finely grated Parmesan (about 1 1/2 cups); 1/8 tsp kosher salt; 1/8 tsp red pepper flakes (optional); 1/2 cup extra-virgin olive oil; 1 lb. rigatoni (bucatini or spaghetti)