1. To make a batter for the fish, stir together 1 cup of the rice flour, all-purpose flour, baking soda, and lemon zest; reserve remaining rice flour for breading.
2. Whisk 2 cups of water into the flour mixture until smooth; set batter aside while you making the coleslaw dressing.
1. To make the dressing, heat a large pan over medium heat. Add onions and mangoes to the pan and cook while stirring for 3-4 minutes, or until onions start to soften.
2. Stir lime juice and sugar into the onions and mangoes and bring the mixture to a boil; remove from heat and pour mixture into a blender or food processor.
3. Blend until smooth.
4. While blending, pour 1 cup of canola oil into the blender in a slow stream; blend until combined.
5. To blanch the mint for the dressing, prepare a small ice bath. Bring a small pot of water to boil; add mint leaves and blanch for 1 minute.
6. Plunge mint into ice bath, strain, and add mint to the food processor and blend; set dressing aside to cool to room temperature.
7. Once dressing has cooled, toss with cabbage, tomato, scallions, and cilantro; season with salt and pepper, to taste, and set coleslaw aside until assembly.
8. Preheat remaining canola oil to 325ºF in a large heavy-bottomed pot over medium heat.
1. Preheat remaining canola oil to 325ºF in a large heavy-bottomed pot over medium heat.
2. To set up a dredging station for the fish, put remaining rice flour in a small bowl; pour reserved fish batter in a second bowl.
3. Cut haddock fillet in half and dredge each piece in the dredging flour, to cat; dip fish into the batter and fry in oil for 2 minutes, or until fish floats.
4. Set fish on a paper towel to absorb excess oil. Repeat with remaining fish.
5. Toast tortilla shells in a large pan over medium heat.
6. To assemble the tacos, add two pieces of fish to each tortilla and spoon slaw over top; serve two tortillas per serving.
7. Note: Leftover dressing will keep for 3-4 weeks if covered and refrigerated.