In a wide pan over medium heat, heat about 1 tablespoon of oil. Add onions and cook until softened.
Add bell peppers and cook until tender crisp.
Add chicken, black beans, and corn. Cook just until heated, gently stirring to combine.
Add spinach and cook just until wilted.
Add chili powder, salt, garlic powder, and pepper. Stir to distribute.
Remove from pan and drain excess liquid in a colander. Allow to completely cool.
Transfer to a bowl and add shredded cheese, tossing to combine.
Separate egg roll wrappers into individual sheets. On a flat working surface, lay the wrapper like a diamond.
Spoon about 2 tablespoons of meat mixture on the middle of the wrapper.
Fold the bottom pointed end of wrapper over filling. Fold side ends of the sheet inward and roll tightly into a log. Wet the pointed edge of the wrapper with a dab of water to completely seal. Repeat with the remaining mixture.
In a pan over medium heat, heat about 2-inches deep of oil to 350 F. Add egg rolls and deep-fry, turning on sides as needed, until golden brown and crisp.
Remove from oil and drain on a wire rack set over a baking sheet. Serve with ranch dressing.