For the salt: Heat 1/4-inch oil in a large, high-sided skillet over medium-high heat (the oil is hot enough when a pinch of cornmeal sizzles when added to the pan). Add the rosemary sprig and fry for 30 seconds until crisp. Using tongs, remove the rosemary sprig and drain on paper towels. Remove the leaves and finely chop to yield 1 tablespoon. Place the rosemary, salt, and lemon zest in a small bowl. Mix with a fork until combined. Set aside.
For the chicken: In a medium bowl, mix together the chicken, garlic, rosemary, lemon zest, salt, and pepper. Add the cornmeal and toss until the chicken is coated. Add 1/2 the chicken to the same skillet used to cook the rosemary and fry until golden and crispy, 2 to 3 minutes on each side. Drain on paper towels. Repeat with the remaining chicken. Sprinkle with the rosemary-lemon salt and serve.