Combine all the Spanish seasoning ingredients in a small bowl and mix well. Cut the lemon in half and slice one half thinly for garnish; set the other half aside to juice later.
Place chicken in a bowl, pour over 2 tablespoons of oil and toss thoroughly to coat. Apply half of the seasoning mixture evenly on both sides of the chicken pieces.
Heat the remaining 1 tablespoon of oil in a large skillet over medium heat. Sear the chicken for about 2 to 3 minutes per side until golden brown, then remove and set aside—it will finish cooking later.
Add the uncooked rice, chicken broth, lemon juice, and the rest of the seasoning mix to the skillet and stir until combined.
Nestle the chicken back onto the rice mixture, cover the skillet, and let cook on low to medium heat for 20 to 25 minutes, until the rice absorbs the liquid and the chicken is fully cooked.
Sprinkle the chopped cilantro or parsley on top, arrange the lemon slices as garnish, and serve immediately.