Cook onions and peppers on the stove until softened.
Add broccoli, carrots, and mushrooms and cook until crisp-tender.
Layer in the slow cooker starting with marinara sauce, then broken lasagna sheets, spinach, cooked vegetables, cheese, and Italian seasoning.
Repeat the layering process for a few layers.
Finish with a layer of broken noodles and marinara.
Cover and set the slow cooker to 'low' for four hours.
