Place the chicken breasts on a clean work surface. Place your palm on top of the breast to anchor it to the cutting board and carefully slice the breast in half lengthwise (parallel to your hand through the center). Alternatively, you can ask the butcher to butterfly the breasts for you. You should have two thin cutlets of chicken. If they are still attached at one end (in the shape of a butterfly), sever it so you have 4 cutlets total (from the 2 breasts). Season the chicken with salt and pepper.
Place the flour in a shallow bowl. Dredge the chicken breast cutlets until fully covered in flour and shake off any excess. Set the coated chicken aside.
In a large skillet over medium high flame, heat a thin layer of olive oil. Once the oil is hot, add 1 tablespoon of butter, and immediately arrange half the chicken in the pan. Cook for 3 minutes, or until a brown crust has formed. Flip the chicken and cook for another 2 minutes. Remove and transfer to a plate. Repeat with the additional chicken pieces, adding more oil and butter as needed and adjusting the heat if any flour debris starts to burn.
Meanwhile, combine the lemon juice, chicken stock, and capers in a 2-cup liquid measure or bowl.
When the chicken is finished, add the lemon slices directly to the pan and sauté over medium-low heat until lightly blistered, 2 minutes. Remove to the plate with the chicken.
Add the spinach to the pan and sauté until wilted, 2 minutes. Season lightly with salt and remove to the same plate.
Pour the chicken stock lemon mixture into the pan and bring to a boil over medium-high heat, scraping up any brown bits the spinach didn’t dredge up. Add the remaining 2 tablespoons of butter to the sauce and carefully return the gluten-free chicken piccata to the pan. Simmer until the dairy-free piccata sauce is thickened slightly, but not fully evaporated, 3 to 5 minutes. Taste for seasoning and add more salt as needed.
Off the heat, tuck the spinach in between the chicken cutlets and garnish with the frizzled lemon slices and fresh parsley. Serve immediately as a complete one pan meal, or alongside rice or your favorite gluten-free pasta.
