Saute' onion,zucchini, and mushrooms in oil until slightly tender. Add salt and mix well. In slow cooker, layer 1/3 of veg. 1/3 of tomatoe sauce and 1/3 of cheese. Sprinkle with oregano, salt and pepper. Repeat layers twice. Cook on low for 6 to 8 hrs.
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ITALIAN VEGETABLE CASSEROLE recipe