Preheat the oven to 180 degrees C. Cut the chicken breast fillets diagonally into strips about 2 1/2cm thick.
Lightly whisk the egg whites together in a shallow dish until just foamy. In another shallow dish, combine the breadcrumbs with the garlic, celery seeds, paprika, chilli powder and half of the pepper then spread out evenly.
Dust the chicken strips very lightly with flour then dip into the egg whites to cover completely. Finally, coat with the seasoned breadcrumbs. Place on greaseproof paper.
In a large non-stick frying pan, heat 1 1/2 teaspoons of the oil over moderate heat. Add one-quarter of the chicken strips and cook for 2–3 minutes or until browned on all sides. Transfer to a large baking tray.
Brown the remainder of the strips, in three batches, using the rest of the oil. Then bake the chicken for about 15 minutes or until tender and cooked through.
Meanwhile, make the salsa. In a bowl, combine the diced tomatoes, mango and remaining pepper. Serve with the chicken bites.