Preheat oven to 425 degrees.
Lightly coat a 9- x 13-inch baking pan with olive oil (you don't need much!). In a large bowl, combine first 12 ingredients (zucchini through red onion); toss to combine then spread in prepared pan.
Bake for 20 to 30 minutes or until zucchini is fork-tender and remaining veggies are nicely roasted and slightly browned; return to the large bowl.
In a large, deep skillet, heat the lemon juice and water over medium-high heat. Add the spinach; cook and stir until wilted (1 to 2 minutes); drain well then add to the roasted vegetables and toss to combine.
Top with grated Parmesan, if desired, and serve.