Set the smoker to 275F using wood chips of choice (alder, apple or cherry are great choices).
Place the fish fillets in the smoker. Smoke the fish until they reach an internal temperature of 145F, about 2 hours. Cool.
In a medium size bowl, make the pico de gallo by mixing together the diced tomatoes, onion, jalapeno pepper and lime juice.
Assemble the tostadas by crumbling some of the fish and spread on a tostada shell. Spoon some of the pico de gallo on top of the crumbled fish. Sprinkle some feta cheese on top. Do this with the remaining tostada shells.