1. Cut a horizontal slit along the thin, long edge of each chicken breast, nearly through to the opposite side. In a small bowl, whisk together lime juice, zest, cilantro, salt, pepper, and sugar. Put chicken breasts and marinade in a large Ziploc bag and seal. Squish the bag around until breasts are well coated. Place the chicken in the refrigerator for at least 1 hour (up to 12 hours).

2. Remove the chicken breasts from the marinade and discard marinade. Open up the slits and stuff each breast with 2 tablespoons shredded cheddar cheese, 1 teaspoon jalapeño, and 1 tablespoon chopped cilantro.

3. Preheat the grill to medium-high heat. Brush the grill lightly with olive oil. Grill chicken until cooked through, about 7 minutes per side. Remove from direct heat and sprinkle remaining shredded cheddar cheese on top of each breast. Cook until cheese is melted. Remove from heat and serve.