Heat the oven to 325°F. Drain the shrimp and pat them dry. Place them in a large bowl with the salt, cumin, garlic powder, lime juice and zest, and olive oil. Toss to combine and set aside to marinate.
Place the cabbage in a medium bowl and toss with a pinch of salt. Set aside. Stir the beans and the salsa verde together in a small pot and place over medium-low heat.
Slice the radishes. Place the tostada shells on a rimmed baking sheet and place in the oven for 6 to 7 minutes.
Prepare any other toppings. Heat a large skillet over medium-high heat for a minute or two, and when it’s hot, add the shrimp. Cook, stirring, for about 3 minutes, until the shrimp have firmed up and turned bright orangey-pink. Remove from heat.
To assemble, put two tostada shells on each plate and spread with a spoonful of sour cream. Spoon beans over each (you'll likely have beans left over). Divide the shrimp and place over the beans. Top with cabbage, radishes, and cilantro. Serve with hot sauce and lime wedges.