Preheat oven to 350° F.
To make Cajun firecrackers, lightly dust chicken breasts with Cajun seasoning. Heat large, oven-proof sauté pan, then add small amount of oil. Add chicken breasts and cook over high heat until one side is blackened, 2 to 3 minutes. Turn in pan; finish in preheated oven 6 to 7 minutes, until chicken is cooked through.
When done, remove from oven, set aside and let cool. When cool, slice chicken breasts crosswise into 1-inch strips.
Open spring roll wrappers and fill as directed below. Fill 2 wrappers only at a time as they dry out quickly. Wrappers not being used should be stored under a wet towel.
For each firecracker: With one corner of wrapper facing you, set 1 strip of chicken in center horizontally. Set four spinach leaves horizontally, just underneath chicken strip, overlapping the leaves slightly.
Roll pointed edge inward, covering filling. Fold in sides, then fold down top piece. When finished, you should have a rectangular-shaped roll that looks like an envelope. When working with the wrappers, roll them tightly so there are no wrinkles but gently as they are delicate. Seal edges with water and a pastry brush.
As you make them, cover with a wet towel or wet paper towels until ready to fry all the rolls.
When all are prepared, drop in hot canola oil that has been heated to 350° F and fry until golden brown on all sides, about 3 to 4 minutes, turning halfway through. Do in batches so as not to overcrowd. Drain off excess oil on paper towel. Slice in half and serve with dipping sauce.