First, prepare the avocado mango salsa. Combine the diced avocado, mango, plum tomato, and cilantro in a bowl. Sprinkle with lime zest and lime juice. Mix well and place in the refrigerator until your ready to construct the tacos.
Season the mahi-mahi with the taco seasoning on both sides, and set to the side. Then, preheat a skillet on medium heat.
Add 1 tablespoon of vegetable oil. Cook the mahi-mahi for 5 minutes, turn over and cook for an additional 5 minutes. Then remove the fish from the pan and set to the side (to keep it warm you can tent the fish with a piece of aluminum foil).
Using the same sauté pan, add in 1-cup canola cooking oil. Increase the heat to high. After the oil has heated for 1-2 minutes, place one white corn tortilla in the skillet. Once it begins to bubble (about 10-15 seconds) turn the corn tortilla over, let it stand for 5 seconds then using tongs fold one end in half. Rotate each side for a few seconds until golden brown. Once the corn tortilla shell is golden brown, remove from the sauté pan and place on a paper-towel lined plate. Repeat until all the taco shells have been cooked.