Preheat oven to 400°F. Heat oil in a large skillet over medium-high heat.

Add onions and sauté for 2 minutes; stir in garlic and chicken and continue to cook for 4 minutes. Add milk and simmer for 2 minutes, or until most of the liquid has evaporated. Stir in ricotta cheese until well blended. Add spinach and cook for 2 minutes, or until wilted.

Remove from heat and let stand a few minutes, or until cool enough to handle.

Spoon pasta sauce on the bottom of a 9x13" baking dish and set aside.

Using a spoon, your hands, or even a piping bag, stuff the prepared chicken mixture into cannelloni tubes. Arrange the cannelloni in a single layer on the bottom of the previously prepared baking dish. Set aside.

In a mixing bowl, combine half and half, parmesan, basil, oregano, nutmeg, salt, and pepper; whisk until thoroughly combined. Pour the half & half mixture over the cannelloni.

Bake in the oven for 18 to 20 minutes, or until top is golden brown and the cream is reduced.

Remove from oven and let stand 3 minutes, or until sauce has slightly thickened.

Spoon the sauce over the cannelloni and serve.