Place poblano chiles over open flame, medium heat, turning until completely blistered. Place blistered chiles in paper bag or a kitchen towel and let them sweat for 15 minutes.
Meanwhile, dry-roast whole tomatoes by placing in a dry skillet over medium heat. Keep turning as they blister and show brown-black spots. At the end, tomatoes should be soft, cooked inside and charred. Transfer tomatoes (do not peel them) to a blender and process until smooth. Set aside.
When cool enough to handle, peel chiles, discard seeds and stems, and dice.
In a large sauté pan over medium heat, sauté onions in the oil for 1 minute, then add zucchini and corn kernels. Sauté for 2 more minutes, then add tomato puree. Reduce heat to a simmer, cook for 2 minutes, then add diced poblano and cheese. Cook for 4 more minutes and season with salt. Serve hot with warm tortillas. Can be served as an appetizer or as a side dish with grilled fish, chicken, meat or brown rice.