Set an extra-large cast iron cast over medium-high heat. Add the butter, onion, garlic, and poblano pepper. Saute and soften for 3-5 minutes, stirring occasionally.
Add the ground cumin and oregano to the skillet. Stir and push the onions to the sides of the skillet.
Add about a third of the chopped squash and bell peppers. Brown for 1 minute. Then push them to the sides of the pan and add another third of the veggies. Cook for 1 more minute. Then push the veggies to the sides and add the remaining squash and peppers. (This method allows each batch of squash and peppers to get a bit of color.)
Season with 1 teaspoon salt and ¼ teaspoon ground black pepper. Brown another minute, then stir in the corn, cilantro, and juice of ½ a lime.
Stir to warm the corn, then turn off the heat. The veggies should be just barely cooked and still firm.
Serve warm with a generous sprinkling of crumbled queso fresco, a dollop of pico de gallo, avocado slices, and extra lime wedges.
Cutting Tips: Use 1 large or 2 small zucchini and yellow squash. Cut lengthwise in thirds, then cut each slice in thirds to create 9 long strips. Cut across the strips to create small even cubes. Chop the peppers in similar sized squares.Do not overcook. It’s better for the vegetables to be slightly undercooked, than soft and mushy.Three Sisters: You can add a 15 ounce can black beans to make a Navajo “Three Sisters” version combining squash, corn, and beans.