In a large bowl, mix together egg, ricotta, ¼ cup Parmesan, oregano, salt and pepper until well combined. Fold in spinach and kale.Prepare sauce: In a large pot on medium, melt 2 tbsp butter. Add onions and cook, stirring occasionally, until onions are translucent, about 4 minutes. Add garlic and cook, stirring constantly until fragrant, about 30 seconds. Add 2 tbsp flour and cook, stirring gently, for 1 minute more or until golden. Slowly add broth, whisking constantly and cook until slightly thickened, about 1 minute more.Place one-third of sauce on the bottom of a 5-qt slow cooker, spreading to cover entire bottom. Top with a single layer of noodles, trimming them to fit if necessary (1 fresh sheet or 2 dried noodles). Spread half of cheese mixture on top followed by half of the butternut squash slices. Top with another layer each of the following: noodles, sauce, cheese, squash, noodles and sauce. Cover slow cooker and cook on high for 2 hours.In the last 45 minutes of cooking, melt remaining 1 tbsp butter in a small saucepan. Add remaining 1 tbsp flour and cook, stirring constantly, until golden, about 1 minute. Slowly whisk in milk and cook, stirring constantly, until thickened, about 1 minute. Remove from heat and stir in remaining ¼ cup Parmesan and nutmeg.Pour sauce over lasagna; cover again and cook for remaining 30 minutes. Turn slow cooker off and allow to stand for 30 minutes before slicing.