Whisk together all Sweet and Sour Sauce ingredients in a medium saucepan. Bring to a boil then reduce to a simmer until slightly thickened. Set aside. (Sauce will continue to thicken as it cools.)
In a large skillet, heat 1 tablespoon oil over high heat. Add chicken and onions and cook until chicken is mostly cooked through, approximately 3 minutes. Add vegetables and pineapple and stir fry over medium-high heat until vegetables are crisp-tender and chicken is cooked through, approximately 2-3 minutes. Add 1/4 cup Sweet and Sour Sauce and mix to combine.
Using a slotted spoon (you don’t want extra moisture), add chicken/vegetables to your food processor and pulse until finely chopped (about 12 pulses).
Position an egg roll wrapper with one point towards you. Place 1/4 cup filling centered in the bottom third of the wrapper. Fold bottom corner over filling then continue to roll up, firmly folding sides toward center over filling as you roll. Moisten top corner with water and press firmly to seal. Repeat with remaining wrappers and filling. (Refer to your egg roll wrapper for a diagram).
Heat oil in a deep stock pot/Dutch oven or deep-fat fryer to 350 degrees F or medium high heat. Fry egg rolls, 4 at a time until golden brown, turning egg rolls a few times while frying. Drain on paper towels.
Serve with reserved Sweet and Sour Sauce. If your sauce has become too thick, simply stir in some water to thin.