Wild Mushroom and Spinach Stuffed Shells

Name: Wild Mushroom and Spinach Stuffed Shells
Ingredients: 6 ounces jumbo shell pasta (20 shells); 1 ¾ teaspoons kosher salt, divided, plus more for cooking pasta; 3 tablespoons olive oil, divided, plus more for baking dish; 1 medium yellow onion, chopped; 3 cloves garlic, chopped; 1 28-oz. can crushed tomatoes; ¾ teaspoon freshly ground black pepper, divided; 8 ounces sliced mixed wild mushrooms (such as shiitake, oyster, and cremini); 5 ounces baby spinach, roughly chopped (5 cups); 1 16-oz. container whole-milk ricotta cheese; 1 cup grated Parmesan cheese