Zucchini, spinach and yellow bell pepper add color and texture to this 300-calorie slow-cooker lasagna. Other veggies work great in this dish, so feel free to use what you have on hand: Sliced mushrooms, yellow squash, sliced red onion, and green bell pepper are all perfect additions. You can prep this lasagna 24 hours ahead of time! Assemble, cover with foil and refrigerate in your slow cooker’s insert. Cook time will take longer if made ahead, so make sure it’s heated through the center.