Prepare Pickled Vegetables at least 30 minutes or up to a day in advance:

1. Peel and shred carrots and place in a heat resistant jar (one you can cover and refrigerate).
2. Place onions in a jar as well as radishes
3. Boil water. Add sugar, garlic. Remove from heat and allow to sit for 10 minutes. Add vinegar and pour over veggies until covered, making sure 1 garlic clove makes it into each jar.
4. Cover veggies and allow to refrigerate for 30 minutes.

Prepare sauce:

1. combine mayo, chili sauce and red pepper flakes
2. allow to rest while preparing fish. 

Make Fish Tostadas:

1. In a large sauté pan, heat oil over medium high heat. Salt and pepper cod and place in skillet. Cook for 4 minutes. Flip fish and cook for 3 more minutes.
2. Remove from heat and transfer to plate. Squeeze juice from 1 lime over fish.
3. Heat tortillas over open flame on stove or on grill turning often so as not to burn. Heat for 30 seconds each.
4. To assemble, spread the mayo mixture on the tortilla and add your choice of pickled veggies. Cut the fish into 6 equal portions and add then top with Cotija cheese and cilantro along with a lime wedge.
5. Continue with remaining tortillas. Serve while warm.