First you’ll need to roast the chiles. Place the chiles under the broiler until blackened, about 5 minutes per side. Place the chiles in a paper sack or plastic food-storage bag, close it tight and let the chiles steam for 20 minutes. Take the chiles out of the bag and gently rub off the skin. Remove the stem and seeds and dice the chiles.
In a large skillet, heat the butter on low heat. Add the onion and while stirring occasionally, cook until the onions are softened and just beginning to darken, about 7-10 minutes. Stir in the garlic and cook for 30 more seconds.
Add to the skillet the squash, salt, and pepper and while stirring occasionally, cook until squash is softened though still a bit crisp, about 7-10 minutes. Stir in the diced green chiles and cilantro. Taste and add more salt and pepper if needed.
Finish with a squirt of lime juice and serve warm.
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