Cook the lentils according to the instructions. Drain and set aside. In a medium pan, roast the walnuts without oil for about 2 minutes or until they're lightly golden. Put the walnuts and the cooked lentils in a food processor and process until chopped. Make sure to leave some texture!
In a medium pan, heat the olive oil over medium heat and sautée the onions for about 3 minutes. Then add the lentil walnut mixture and stir in the tomato paste. Cook for 2 minutes. Add the diced tomatoes and the spices (paprika powder, cumin, oregano, salt, and pepper).
Make the sour cream: Drain the cashews and put all ingredients in a food processor and process until smooth. Season with salt and pepper.
In a large bowl, combine the lettuce, the corn, the tomato, the avocado, the salsa, and the black beans. Serve with the lentil walnut meat, cashew sour cream, and the nachos on top and sprinkle with green onions, red onions, and fresh cilantro.