1 pound pasta, such as fusilli
Coarse kosher salt
1 tablespoon olive oil
1 pound chicken breast, diced into 1-inch pieces
Freshly ground black pepper
10 ounces baby spinach, about 8 packed cups, roughly chopped
2 shallots, diced
1/4 cup unsalted butter (1/2 stick)
1/3 cup flour
2 cups 2% milk
1 cup nonfat yogurt
4 ounces grated Parmesan cheese, divided
1 lemon, zested
Heat the oven to 350°F. Lightly grease a 9x13-inch baking dish, or two 9x9-inch baking dishes.
Heat a large pot of water to boiling. Salt generously. Add the pasta and cook according to package directions. When it reaches al dente, drain.
While the pasta water is boiling and the pasta cooks, heat a deep sauté pan over high heat and add the olive oil. When it shimmers, add the chicken pieces and sprinkle lightly with salt and pepper. Cook for about 2 minutes, not moving the pieces and letting them brown, then stir and brown the other side. Add the chopped greens, letting handfuls wilt down first if necessary, and cook just until half wilted. Spread in the prepared baking dish (or divide between two dishes). Add the diced shallots and toss.
Wipe out the sauté pan and return to medium heat. Add the butter and melt. Whisk in the flour and cook for 3 minutes. Slowly whisk in the milk, whisking vigorously to avoid lumps. Cook for 3 to 5 minutes, whisking constantly, until the sauce thickens. Remove from the heat and stir in the yogurt, 3/4 of the Parmesan cheese, and lemon zest. Add 1 teaspoon salt and a generous quantity of black pepper.
Toss the pasta with the chicken and spinach in the baking dish (or dishes), using a spoon or your hands to mix thoroughly. Pour the sauce over top and mix. Sprinkle the top with the remaining Parmesan cheese.
Bake for 25 minutes or until hot through and slightly browned on top.