Slice 18 pieces of cucumber 1/8 in 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 ring mold) and fry to crispy; dry on a paper towel and add salt a.s.a.p.
Mix mayo & chipotle with hand mixer; drain cucumber and add lime juice & sugar and let stand; as it stands thinly slice Serrano’s & pick cilantro
Slice tuna into thin slices (1/4 in thick or ~ 5 oz.)
Lay out all tostadas on a large platter & 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 & cilantro. Add a lime wedge and an extra squeeze of flavor.