In a large skillet heat 2 tablespoons of the butter and the olive oil over medium heat until sizzling. Add onion; cook and stir 4 to 5 minutes, or until softened and translucent. Add garlic; cook and stir until fragrant, about 1 minute. Add poblano chile, bell pepper, salt and pepper; cook and stir 4 to 5 minutes more until vegetables have softened.
Add zucchini and yellow squash; cook and stir 4 to 5 minutes, until softened. Stir in green onions and corn; simmer, undisturbed 5 minutes, or until most of the liquid has evaporated. Stir in remaining tablespoon of butter until melted; season to taste with salt and pepper. Transfer to serving bowl or platter and sprinkle with cotija cheese and cilantro if using. Serve immediately, with lime wedges if desired.