Cook the cannelloni following the instructions on the package. Set aside.

Pour the olive oil on a pan and stir-fry the garlic and onion, then add the mushrooms and continue cooking until it dries up.

Add the spinach and the chopped walnuts, and cook for 3 more minutes, occasionally stirring.

Mix the ricotta cheese with the spinach filling and season it with salt and pepper to taste. Put the mix in a pastry bag/piping bag* to fill the cannelloni.

Preheat the oven to 180 °C.

Place the cannelloni in a casserole and sprinkle the grated Manchego cheese on top. Cover the casserole with the aluminum foil.

Bake the cannelloni for 20 minutes, then remove the aluminum foil and continue cooking for 5 more minutes or until the cheese is gratin.