Start the water for the pasta. Once the water boils, cook the shells in well salted water according to package directions. Cook for two minutes less than is stated on the package.

In the meantime, prepare the filling. Heat a large frying pan over medium heat, then add the olive oil.

Add the mushrooms to the pan and spread into an even layer. Cook, avoiding stirring, for 3-4 minutes, or until browned.

Add the onion and cook for another 1-2 minutes. Add the garlic, salt, and pepper, and cook for another minute.

Take the pan off the heat and add the baby spinach. Stir to wilt the spinach with the residual heat from the pan.

Add the cashew cream cheese and stir through. Set aside until the pasta is ready.

Drain the pasta (don't rinse it). Working carefully, fill each shell with a heaping tablespoon of the filling. Place each filled shell into the tomato sauce in the baking dish, repeating until all of the shells are filled.

Bake for 10 minutes. After this time, the pasta should be a bit bigger, but not browned.

Remove from the oven, add any toppings you'd like, and serve immediately. Leftovers keep well for a day or two in a sealed container in the refrigerator.