Bring a large pot of salted water to a boil. Add the pasta and cook until al dente. Drain and return to the pot. Set aside.

Preheat the oven to 350ºF. Grease a shallow 2-quart baking dish with nonstick cooking spray.

Meanwhile, heat the olive oil in a sauté pan over medium heat. Add the onion and cook until very soft and starting to brown, about 10 minutes. Add in the spinach and cook until wilted, an addition 1-2 minutes.

While the onions are cooking, melt the butter in a medium saucepan. Add the flour and whisk to combine. Cook for 1 minute. Slowly whisk in the milk, then season with salt and pepper. Add a dash of nutmeg and the Dijon mustard. Bring the mixture to a boil, whisking very frequently. Continue to cook until thickened. Remove from the heat and stir in the ricotta and garlic and herb cheese.

Stir the cheese sauce into the pot with the shells. Add in the onion/spinach mixture and the cubed ham and stir to combine. Pour the mixture into the prepared baking dish. Sprinkle the Parmesan on top.

Bake the casserole for 25-30 minutes, or until bubbly.