Place all of the vegetables in a large bowl and season well, tossing with salt, pepper, and a pinch of crushed red pepper. Heat a large heavy skillet over medium high heat and add one tablespoon of the olive oil. Cook the zucchini in two batches -- one layer each, sautéing until browned on one side. Turn and cook the second side. Remove to the bowl. Repeat, adding a little more olive oil if needed. Drizzle in the second tablespoon of olive oil, and add the peppers, onions, and mushrooms, cooking and stirring regularly until vegetables are browned and nearly tender. Stir in the garlic, tomatoes, and a pinch of crushed red pepper, cooking another minute or two. Tip the bowl of cooked zucchini back into the skillet, stir, and warm through. Cover to keep warm until needed.