For marinara sauce – In a 4-quart saucepan, cook onion and garlic in olive oil until tender. Stir in sugar, basil, tomatoes with their liquid and paste. Heat to boiling, reduce heat, cover, and simmer 20 minutes, stirring occasionally.
For lasagna – Arrange eggplant slices in a single layer on baking sheet and brush with olive oil and pepper. Roast at 400 for 10-15 minutes until soft.
Combine ricotta cheese and egg. Add herbs and 1/2 cup mozzarella cheese. Add chopped spinach. Mix well.
Pour half of marinara sauce into a 9×13 baking dish
Layer: half the eggplant, half the spinach/ricotta mixture, all the zucchini slices, 1/2 cup mozzarella. Add another layer: rest of spinach/ricotta mixture, rest of eggplant, rest of marinara. Top with 1 cup or more mozzarella.
Cover with foil but make sure foil isn’t touching the cheese. Bake at 400 for 45 minutes covered, then remove foil and bake for another 10-15 minutes. Let salsagna cool fo 15-20 minutes before cutting.