Preheat oven to 400 degrees. Heat olive oil in a 12" cast iron skillet over medium-high heat until shimmering, then add squash, onion, garlic, chipotle, and zucchini. Saute for 12-13 minutes, stirring occasionally, then spread squash mixture out across the bottom of your skillet.
While squash is sauteing, whisk together eggs, sour cream, sea salt, pepper, oregano, and parsley until well blended.
Pour the egg mixture into the skillet on top of the cooked squash and continue cooking over medium-high heat just until the edges start to set (about three minutes).
Turn off heat and top eggs with shredded cheddar and sliced tomato, then move the skillet into the oven and bake at 400 degrees for 15 minutes, or until frittata is set.
Broil for another two minutes to brown, then let sit for at least five minutes before slicing.
I used one smallish zucchini and two little squash in my frittata here. The one chipotle pepper when diffused through the whole big frittata adds only very mild heat (I might actually go with two next time!), but you can substitute a little crushed red pepper if you prefer.
Summer Squash + Tomato Frittata from Mashup Mom: https://www.mashupmom.com/summer-squash-tomato-frittata-low-carb-gluten-free/