In a large skillet, heat 1 tablespoon of the oil over medium heat.
Add the onion, garlic, peppers, and mushrooms; sauté until the vegetables are tender. Remove to a separate bowl.
Heat the remaining tablespoon of oil and sauté the zucchini and yellow squash until softened.
Stir in the pepper mixture and tomato purée; cook over medium-low heat for about 10 minutes.
Stir in the scallions, plum tomatoes, cilantro, basil, and parsley.
Let simmer 5 to 10 minutes, stirring occasionally until heated through.
Serve warm.