Ingredients

• Cooking spray
• 2 tbsp. extra-virgin olive oil
• 1 large yellow onion, chopped
• 2 cloves garlic, minced
• 1 lb. sweet Italian sausage, casings removed
• Kosher salt
• Freshly ground black pepper
• 1 (24-oz.) jar marinara
• 1 (5-oz.) package baby spinach
• 16 oz. ricotta
• 1 large egg, beaten
• 3/4 c. freshly grated Parmesan, divided
• 1 tsp. dried oregano
• 3 large sweet potatoes, peeled and sliced 1/8"-thick (about 2 lb.)
• 1 1/2 c. shredded mozzarella
• Freshly chopped parsley, for garnish

Description

1. Preheat oven to 375° and grease a 9"-x-13" baking dish with cooking spray. In a large skillet over medium heat, heat oil. Add onions and cook, stirring occasionally, until soft, 5 minutes. Add garlic and cook until fragrant, 1 minute more. Add sausage and cook, breaking up with a wooden spoon, until no longer pink, about 6 minutes. Season with salt and pepper. 
2. Pour in marinara and bring to a simmer. Cook until sauce thickens slightly, 5 minutes. Add spinach and cook until wilted, 2 minutes. Remove from heat. 
3. In a large bowl, combine ricotta, egg, ½ cup Parmesan, and oregano. Season with salt and pepper. 
4. Spread a thin layer of marinara mixture evenly across bottom of baking dish. Layer a third of the sweet potatoes on top of sauce, slightly overlapping. Spread about a third of the ricotta mixture over sweet potatoes and top with a third of the remaining meat sauce. Repeat to make 2 more layers. Top with mozzarella and remaining ¼ cup Parmesan. 
5. Cover with foil and bake until sweet potatoes are almost cooked through, about 45 minutes, then remove foil and bake until sweet potatoes are fork-tender and cheese is golden, 15 minutes more. 
6. Let lasagna rest 10 minutes. Garnish with parsley before serving.