Baked Ziti with Spinach and Tomatoes

I made this the other night for the missionaries and we all loved it! I was worried when I put in so much spinach that it might taste a little odd, but it was really great! From one of my favorite sites, epicurious via stephmodo.

3/4 pound hot Italian sausages, casings removed (I used ground turkey and added some flavoring...)
1 medium onion, chopped
3 large garlic cloves, chopped
1 28-ounce can diced peeled tomatoes
1/4 cup purchased pesto sauce

10 ounces ziti or penne pasta (about 3 cups), freshly cooked (you could add a bit more...)
8 cups ready-to-use spinach leaves (about 2/3 of 10-ounce package)
6 ounces mozzarella cheese, cubed
1 cup grated Parmesan cheese (about 3 ounces)

Heat heavy large saucepan over medium-high heat. Add sausage, onion and garlic and sauté until sausage is cooked through, breaking up meat with back of spoon, about 10 minutes. Add tomatoes with juices to pan. Simmer until sauce thickens slightly, stirring occasionally, about 10 minutes. Stir in pesto. Season sauce with salt and pepper. (Can be prepared 1 day ahead. Cover and refrigerate. Bring to simmer before continuing.)

Preheat oven to 375° F. Lightly oil 13 x 9-inch glass baking dish. Combine pasta, spinach, mozzarella and 1/3 cup Parmesan cheese in large bowl. Stir in hot tomato sauce. Transfer mixture to prepared baking dish. Sprinkle remaining 2/3 cup Parmesan cheese over. Bake until sauce bubbles and cheeses melt, about 30 minutes.