In a blender canister or small bowl of a food processor, combine the ranch dressing, sour cream, cilantro, avocado, lime juice, and salt. Puree on medium-high speed for about 1 minute, until smooth and the cilantro is finely chopped. Place the sauce in a bowl or jar, cover, and chill until ready to serve. The sauce will stay vibrant for a day or two if you want to make it in advance.

Heat a large skillet over medium heat. Add the vegetable oil, then onion and bell pepper. Cook, stirring occasionally, for about 5 minutes, until slightly softened.

Add the spinach, corn, and jalapeno (if using), and cook for 2 more minutes. Add the cumin, chili powder, garlic powder, salt, and pepper and cook for 1 minute, stirring frequently, until the spices are fragrant. Remove from the heat and stir in the black beans and chicken.

Working with one egg roll wrapper at a time, position the wrapper in front of you with a corner pointing up, so that it makes a diamond shape. Brush the two sides pointing to the top with water. (Keep the wrappers in their package or covered with a damp paper towel or kitchen towel while you work. Otherwise, they can dry out and become brittle.)

Spoon ¼ cup of the chicken mixture in the center of the wrappers. Top each with 1 to 1½ tablespoons of grated cheese. Fold the bottom corner up over the filling. Fold the two side corners over the filling to meet each other in the middle, then roll up to the top corner and gently press to seal. Set aside, covered with a damp towel as you roll the remaining egg rolls.

In a large pot, add enough oil until it is 1 inch deep. Attach a candy or deep fry thermometer, and heat the oil 375°F over medium heat. Meanwhile, line a plate or tray with a few layers of paper towels.

Fry 3 to 4 egg rolls at a time, for about 3 minutes total, turning occasionally with a slotted spoon or spider. Remove them from the oil and drain on the paper towels for a few minutes. Serve while the rolls are hot and crispy with the avocado ranch dipping sauce.