Prepare your slow cooker by lining it with a specially designed slow cooker liner. This will make the dish cook evenly without sticking to the sides.
In a small bowl, combine the crushed tomatoes, garlic, salt, oregano, basil, rosemary, thyme, and pepper. Stir to combine and set aside.
In another small bowl, combine the ricotta, Parmesan cheese, and egg. Use a spoon to cream the mixture together. Set aside.
Pour1/2 cup of the tomato sauce mixture into the slow cooker to coat the bottom of the pan.
Top the sauce with a layer of lasagna noodles. You'll want to break them to fit them in a single layer across the entire crock.
Then spread 1/3 cup of the tomato sauce mixture over the noodles.
Top thatsauce with 1/2 of the sliced mushrooms, diced peppers, and spinach.
Sprinkle 1/3 of the mozzarella cheese over the veggies.
Add another single layer of broken noodles.
Top the noodles with the ricotta mixture. Spread into an even layer over the pan.
Add another single layer of broken noodles.
Top those noodles with 1/2 of the remaining tomato sauce and all the remaining veggies.
Sprinkle 1/2 of the remaining mozzarella over the veggies before adding a final layer of lasagna noodles.
Top the final layer of noodles with the remaining tomato sauce, followed by the remaining mozzarella cheese.
Cover with the lid and set the slow cooker to high for 2 1/2 - 3 hours.
The sauce should be bubbly and the noodles should be tender when done.
Remove the lid and allow to set for 15 minutes before serving.