Meanwhile, heat remaining 1 tablespoon olive oil in a large skillet over medium heat. Add onion and cook, stirring occasionally, until it begins to soften, about 3 minutes. Add mushrooms to the pan and cook until softened, about 5 minutes. Season with ¼ tsp. kosher salt and freshly ground black pepper. Add garlic and Italian seasoning; cook, stirring, for about 1 minute. Add kale and cook, stirring, until wilted, 2-3 minutes. Stir in marinara sauce; cook at a low simmer for 10 minutes.