Beat eggs with water in a shallow bowl. Place bread crumbs into a separate shallow bowl.
Dip an eggplant slice into beaten eggs on both sides and gently press into crumbs to coat. Set aside on a plate. Repeat with remaining eggplant and zucchini slices. Let coated vegetables rest about 5 minutes to set the coating.
Pour canola oil into a large skillet, filling pan to at least 2 inches deep with oil. Heat oil on medium-high heat until oil is almost smoking, about 10 minutes.
Fry 5 to 7 slices of eggplant and zucchini per batch in the hot oil until golden brown, 3 to 5 minutes per side. Drain on a plate lined with paper towels. Repeat frying remaining coated vegetables.
Pour about 1/2 cup spaghetti sauce into the crock of a slow cooker. Lay slices of eggplant and zucchini over sauce; top with about 1/4 cup mozzarella cheese and 1/4 cup Parmesan-Romano cheese blend over vegetables. Repeat layers of sauce, eggplant and zucchini slices, and cheese. When all slices of eggplant and zucchini have been layered, top with any remaining sauce. Sprinkle with Parmesan cheese.
Cook on Low until sauce is bubbling, 6 to 8 hours. Let cool 10 to 15 minutes before serving.
I did this in a slow cooker so that I could leave the house and not leave the oven on. Since the eggplant and zucchini are already cooked, it's really just a matter of how long you want to warm up the sauce and melt the cheese. For the sauce, I made it before I started frying. I improvised and added diced onion, minced garlic, chopped mushrooms and fresh diced roma tomatoes. This was essentially my stock, and I added 2 1/2 jars of already-prepared spaghetti sauce. I let this all simmer on low until I was done frying and ready to put it in the cooker.
The nutrition data for this recipe includes the full amount of the breading ingredients. The actual amount of the breading consumed will vary. We have determined the nutritional value of oil for frying based on a retention value of 10% after cooking. The exact amount will vary depending on cooking time and temperature, ingredient density, and the specific type of oil used.
Try using a liner in your slow cooker for easier cleanup.