Boil potatoes for 20-25 minutes, until tender but not mushy. Drain and quickly place into a large bowl with cold water and ice (ice bath). Let potatoes sit in cold water for 3-4 minutes to halt the cooking process.
Drain potatoes once more and chop them into 3/4" chunks. Set aside.
Heat olive oil in a medium skillet over medium-high heat. Add spam slices and brown each side for 2-3 minutes. Remove and place spam onto a cutting board. Let them cool for at least 5 minutes before cutting into bite-sized pieces.
Combine mayonnaise, lemon juice, Dijon mustard, salt, pepper, paprika, onion powder, hot sauce, and granulated garlic in a large bowl. Add chopped 3/4 each of the green onions and parsley. Stir and adjust salt as needed.
Add potatoes, chopped spam, and 2 chopped eggs to the bowl. Gently fold to combine with dressing.
Transfer Hawaiian potato salad to a serving bowl. Garnish with the remaining 1/4 each of green onions, parsley, and the remaining egg cut into fourths.
Cover the dish with plastic wrap, and place it in the refrigerator for 2-3 hours before serving.