Season fish with salt and pepper, and dust with flour. Heat a skillet and add canola oil to it. Saute the fish until brown on both sides. Remove from the pan and place in a deep pan.
Remove some of the canola oil from the saute pan, and lower the heat to low, add all the vegetables and cook until soft and translucent. Add the ketchup and cook 1 more minute.
Remove from the heat and add all other ingredients, except the avocado. Cover the fish with all ingredients and allow to cool to room temperature. Cover and place in refrigerator for 2 days. Serve with avocado slices.