In a frying pan, heat 2 inches of oil to 360 degrees F.
Fry tortillas, 1 at a time, until crispy, about 2 minutes(do not fold tortilla). Drain on paper towels and set aside.
In a baking dish that will hold the salmon in 1 layer, spread half of the salt over the bottom. Arrange salmon on top of salt then cover with remaining salt. Bake for about 8 minutes. The salmon should be pink and moist in the center; insert a knife tip through salt and into a piece of fish to check. Remove salmon from oven and allow to cool slightly. Lift off and remove salt crust with a spatula. Break up salmon with your fingers and place in a bowl; drizzle with a little bit of the vinaigrette. If desired, add cilantro leaves.
Place a crisp tortilla on each plate. Top with a ladleful of black beans then with a layer of salmon. In a bowl, lightly dress the arugula with remaining cumin vinaigrette. Add sesame seeds and toss well. Place a small mound of greens on each tostada and sprinkle with goat cheese. Place a lime wedge alongside and drizzle with lime-cumin creme fraiche. Serve.
Combine vinegar, lime juice, cumin, salt, and pepper in a bowl, and mix well. Whisk in the oil until emulsified. Set aside until ready to use.;
Vegetarian Black Beans:
In a large pot, bring black beans to boil in water to cover by 2 inches. Add half the onion, the celery and the bay leaf. Reduce heat and simmer until beans are tender, 1 1/2 to 2 hours. Strain and reserve liquid.
In same pot, heat olive oil and add bell pepper, remaining onion, garlic, green onions, basil, cilantro, soy sauce, lemon juice, cumin, cardamom, salt, and pepper. When vegetables are tender, add the beans and the reserved cooking liquid and simmer until reduced by half. Beans can be prepared up to 2 days ahead and refrigerated. To use, ladle out amount desired and heat until warmed through.