Heat a skillet over medium-high heat. Sprinkle chicken with 1/4 teaspoon salt and 1/8 teaspoon pepper. Add 1 tablespoon olive oil to pan; swirl. Add chicken; cook 4 minutes on each side or until done. Transfer to a cutting board.
Combine pecans, juice, onions, remaining 1/4 teaspoon salt, and remaining 1/8 teaspoon pepper in a mini food processor; pulse until finely chopped. Add remaining 2 tablespoons olive oil; pulse to combine. Transfer mixture to a bowl; stir in cheese.
Slice chicken across grain. Place on 4 plates; top with gremolata.