To make the chimichurri sauce in a blender or food processor, combine olive oil, red wine vinegar, parsley, garlic, jalapeno, oregano, salt, and pepper and blitz until everything is finely chopped and emulsified.
1/3 cup olive oil, 2 Tablespoons red wine vinegar, 1/2 cup fresh flat-leaf parsley, 4 cloves garlic, 1/2 jalapeno pepper, 3/4 teaspoon dried oregano, 1/2 teaspoon kosher salt, pinch black pepper
To instead make chimichurri by hand, finely dice the parsley, garlic, and jalapeno, then combine these with the olive oil, vinegar, oregano, salt, and pepper in a small bowl. Stir well.
However you make it, the chimichurri can be prepped up to 24 hours ahead and stored in the fridge. This will actually just let the flavors deepen and meld more.
To start the skillet, spoon about half of the chimichurri out into a shallow bowl or baking dish, reserving the rest to serve later. Nestle chicken breasts into the dish to coat. Marinate at room temperature for at least 10 minutes, or covered in the refrigerator for up to 10 hours.
4 thinly-sliced boneless skinless chicken breasts
While the chicken marinates, warm a very light drizzle of olive oil in a large cast-iron skillet over medium-high heat. When hot, add the asparagus and season it with a light sprinkle of salt and pepper. Cook for 3-4 minutes, tossing occasionally, just until crisp-tender and bright green. Remove asparagus to a plate and set aside.
1-2 teaspoons olive oil , 1 pound asparagus, kosher salt and black pepper
Add marinated chicken to the skillet, discarding the sauce that was used as a marinade. Cook for 3-4 minutes on each side, until the outside is golden and the inside is cooked through. Return asparagus to the skillet, spoon some of the reserved chimichurri over everything, and serve with additional chimichurri at the table.