1 tablespoon lime zest plus 2 tablespoons fresh lime juice
1 teaspoon freshly ground black pepper
In a medium stockpot, bring 6 cups water plus 1 tablespoon kosher salt to a boil. Place the corn into the stockpot and boil for 5 minutes. Remove the corn and pat dry.
Oil a grill pan and heat it over medium-high heat. Add the corn and let cook, using tongs to turn the ears every minute or so, until various kernels are charred, about 10 minutes. Set the corn aside to cool.
In a medium skillet, melt the butter over medium heat. Add the onion and sauté until tender and translucent, 8 to 10 minutes. Transfer the onion to a plate to cool for about 10 minutes.
Carefully remove the corn kernels by standing each cob vertically and cutting down along the cob on all sides. Slice the cherry tomatoes and mozzarella pearls in half, and dice the avocado into 1/2-inch pieces.
In a medium bowl, combine the corn, onion, cherry tomatoes, mozzarella, and avocado. Sprinkle with the cilantro, lime zest, lime juice, pepper, and remaining 1 teaspoon salt and gently toss to combine.
Chill the salad for about 1 hour before serving.
Store the leftovers in an airtight container in the refrigerator for up to 3 days.