Cook the brown rice. Rinse 1 cup of brown rice under cool water.
Add it to a pot with 2 to 2.25 cups water and a pinch of salt. Bring to a boil, then cover and simmer on low until tender, about 35–45 minutes. Fluff and keep warm.
Prep the chicken. Pat the chicken dry and slice large breasts in half horizontally to create thinner cutlets.
Season both sides generously with salt and black pepper.
Heat the pan. Set a large skillet over medium-high heat and add 1 tablespoon of olive oil. When it shimmers, add the chicken in a single layer. Don’t crowd the pan—work in batches if needed.
Get a golden sear. Cook the chicken 3–4 minutes per side, until lightly browned and nearly cooked through.
Transfer to a plate and tent loosely with foil.
Sauté the garlic. Reduce heat to medium. Add the remaining 1 tablespoon olive oil and the minced garlic. Stir for 30–45 seconds until fragrant.
Do not let it burn.
Build the sauce. Pour in the chicken broth, scraping up any browned bits. Stir in lemon zest, lemon juice, Dijon mustard, honey, and a pinch of red pepper flakes if using. Simmer 2–3 minutes to meld.
Finish the chicken. Return the chicken and any juices to the pan.
Simmer gently for 3–5 minutes, spooning sauce over the pieces, until the chicken is cooked through and the sauce slightly reduces. Adjust salt and pepper to taste.
Add herbs and greens. Turn off the heat. Stir in chopped parsley.
If using spinach, fold it into the warm sauce until just wilted.
Plate and serve. Spoon brown rice into bowls, top with chicken, and ladle over plenty of lemon sauce. Add extra lemon wedges and herbs if you like.