Slice 18 pieces of cucumber 1/8 inch thick and place in a small mixing bowl. Add kosher salt and let stand for 10 -12 minutes as to leach out any liquids from cucumber.
Bring up vegetable oil to 350 degrees.Check with candy thermometer, once 350 achieved drop in 9 pieces of tostadas (cut from ringmold) and fry to crispy; dry on a paper towel and add salt ASAP.
Mix mayo & chipotle with hand mixer; drain cucumber and add lime juice & sugar and let stand; as it stands thinly slice serranos & pick cilantro.
Slice tuna into thin slices (1/4 inch thick or 5 ounce.)
Lay out all tostadas on a large platter and put a small dollop of chipotle mayo. Add 3 pieces folded cucumber on top of mayo.
Place soy sauce in small bowl and roll tuna slices in the bowl to season only for a few short seconds; place tuna on cucumbers.
To garnish add sliced jalapeno and cilantro. Add a lime wedge and an extra squeeze of flavor.