Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius). Prepare a large square or round Pyrex dish with high sides. Spray with cooking spray and set aside.

Place onion on bottom of pan in single layer.

Slice zucchini in a food processor. Lay zucchini slices, alternating colors, either in rows (for a square pan) or in concentric, overlapping circles (for a round pan), filling the whole dish. Sprinkle with dried cranberries and raisins.

Mix lemon juice, salt, pepper, sugar, and walnut oil in a small bowl. Drizzle all over the zucchini.

Cover and bake for approximately 40 minutes or until cooked through and soft. You can uncover the dish during the last five to 10 minutes of baking to crisp the edges a bit.