HEAT oil in large skillet on medium heat. Add mushrooms and peppers; cook and stir 3 min. Remove from heat. Add spinach; stir until wilted. Stir in pasta sauce.
MIX egg, ricotta, 1-1/2 cups shredded cheese and 2 Tbsp. Parmesan until blended.
ADD 1-1/2 cups sauce to slow cooker; top with layers of half each of the noodles (broken to fit) and cheese mixture. Cover with 2 cups sauce. Top with remaining noodles (broken to fit), cheese mixture and sauce. Cover with lid.
COOK on LOW 4 to 5 hours (or on HIGH 2 to 3 hours) or until liquid is absorbed. Sprinkle with remaining cheeses; cook, covered, 10 min. or until shredded cheese is melted.
serving size = 1/8 recipe (294 g)