Put the cashews in a 2-cup measuring glass. Cover with hot water and set aside for at least 30 minutes.
Heat up a large, deep-sided skillet. When warm, add the olive oil and heat until shimmering. Add the onions and 1 tsp of salt and reduce the temperate to medium-low heat. Allow the onions to cook until lightly browned. About 12-15 minutes.
Add the garlic, basil, parsley, oregano and crushed red pepper. Continue to cook until fragrant. About 1-2 minutes.
Increase the heat to medium and add carrots and celery. Stir to combine and sauté for 1-2 minutes.
Add the tomato paste and stir to combine. Sauté until the tomato paste becomes a dark red. About 2-3 minutes.
Add the red lentils, diced tomatoes and 1 cup of water. Cover and simmer on medium-low heat until the lentils are soft and the water has been mostly absorbed. Stir occasionally. About 20 minutes.
While the red lentil bolognese is simmering, prepare the pasta shells in accordance with the package directions.
Remove the lid from the lentil bolognese and add the spinach and 1 tbsp fresh lemon juice. Stir to combine and set aside.
Drain and rinse the cashews. Combine the cashews with 3/4 cup of water, 1 tbsp fresh lemon juice, the garlic clove, 1 tsp salt and the nutritional yeast. Blend until creamy.
Stir 1 cup of the cashew cream sauce into the red lentil bolognese.
Prepare each serving bowl with a layer of the red lentil bolognese on the bottom. Stuff the cooked pasta shells with the remaining bolognese and nestle them into the spread of bolognese sauce. Drizzle the remaining cashew cream over the stuffed shells and season with fresh ground pepper and crushed red pepper to taste.