Preheat oven to 400°F. Cut skirt steak into 4 pieces so they fit comfortably in your skillet. Pat dry and season with a generous pinch of salt, and pepper. Let sit at room temp while you make the chimichurri.
In a medium bowl, combine peaches, parsley, cilantro, mint, shallot, oregano, olive oil, and vinegar. Stir well and season with salt to taste. Set aside.
Heat a cast-iron skillet over high heat until very hot. Add avocado oil and heat until shimmering. Working in batches if needed, sear steak pieces 1 minute per side to build a crust. Transfer to a sheet pan fitted with a rack or lined with foil. Deglaze the golden brown bits from the pan with 1/2 cup of water and reduce until thick. Pour this onto the steaks before putting in the oven.
Bake in the oven for 3 minutes at 400°F, until internal temp reaches about 125°F for medium-rare.
Rest 7-10 minutes under loose foil. Slice steak thinly against the grain and spoon peach chimichurri generously over the top. Serve family-style.