Step 1: Prepare the Dip
In a small bowl, mash half of the avocado until it is completely smooth and creamy. Reserve the remaining avocado half for another use. Whisk the mashed avocado with the mayonnaise, buttermilk, and ranch seasoning until the dip is smooth and uniform. Cover the bowl and refrigerate the avocado ranch dip until you are ready to serve.

Step 2: Mix the Filling
In a medium bowl, combine the finely chopped rotisserie chicken, shredded Monterey Jack cheese, thawed corn, black beans, spinach, red bell pepper, scallions, finely chopped pickled jalapeño, taco seasoning, and kosher salt. Stir all the ingredients well until they are thoroughly combined.

Step 3: Assemble the Eggrolls
Lay a large flour tortilla flat. Place about 1/2 cup of the filling mixture slightly below the center. Fold in the left and right sides of the tortilla over the filling, then roll the tortilla up very tightly from the bottom. Use a toothpick to secure the seam shut. Place the finished eggroll on a large plate and repeat this process with the remaining tortillas and filling.

Step 4: Heat the Oil
Pour vegetable oil into a 12-inch cast-iron skillet to a depth of 1/2-inch. Heat the oil over medium-high heat until a thermometer registers 350°F (175°C), which usually takes about 8 minutes.

Step 5: Fry the Eggrolls
Carefully add 3 to 4 eggrolls into the hot oil, always placing them seam side down first. Cook until the eggrolls are golden brown and crispy all over, about 3 to 4 minutes total, flipping them halfway through cooking.

Step 6: Drain and Serve
Use tongs to transfer the fried eggrolls to a plate lined with paper towels to drain any excess oil. Repeat the frying process with the remaining eggrolls. Before serving, be sure to remove all toothpicks. Slice each eggroll diagonally and serve immediately with the chilled avocado ranch dip.