Heat oil in large skillet on medium heat. Add squash, mushrooms and onions, cook and stir 3-5 min. or until vegetables are tender. Stir vegetables into sauce.
Mix ricotta together ricotta cheese, egg, mozzarella and 1/4 cup Parmesan cheese.
To assemble, spoon 1/2 of the vegetable mixture into bottom of slow cooker. Top with half the noodles (broken to fit) and half the cheese mixture. Repeat for second layer.
Cover slow cooker with lid and cook on HIGH for 2 to 3 hours or LOW setting 4 to 5 hours or until liquid is absorbed and lasagna is hot.
Turn slow cooker off and let stand 10 min. Sprinkle with remaining Parmesan before serving.
Note: No need to cook the noodles for this recipe. The noodles become tender when slow cooked in the sauce.