On a 6-quart Instant Pot, select Normal/Medium Sauté. Add 2 tablespoons of oil and heat until shimmering. Add the panko, ¼ teaspoon of pepper flakes and ½ teaspoon each salt and black pepper. Cook, stirring constantly, until the panko is deep golden brown, 3 to 4 minutes. Transfer to a small bowl. Add the lemon zest and ¼ cup parsley, then toss to combine; set aside. With the pot still on Normal/Medium Sauté, add the remaining 2 tablespoons oil. Heat until shimmering, then add the onion. Cook, stirring often, until softened, about 5 minutes. Stir in the remaining ½ teaspoon pepper flakes, 1½ teaspoons salt, 1 teaspoon black pepper, the lentils and 6 cups water. Select More/High Sauté and bring to a boil. Cook for 10 minutes, stirring occasionally, then stir in the pasta and tomato puree.