Toss the shrimp with the cumin, garlic powder and chili powder in a medium bowl.
Combine the sour cream, 1/4 cup of the cilantro and 2 tablespoons of the lime juice in a small bowl.
Heat 1/4-inch canola oil in a large skillet over medium-high heat until hot. Fry the tortillas, one at a time, for 45 to 60 seconds or until puffy, lightly browned and slightly crisp, turning once. Drain on paper towels.
Discard the excess oil and heat the skillet over medium heat until hot. Add the shrimp; cook for 3 to 4 minutes or until the shrimp turn pink.
To assemble the tostados, spread guacamole over tortillas. Top with the shrimp. Sprinkle with the Pico de Gallo, remaining lime juice, green onions, tomato and remaining cilantro. Drizzle with the cilantro-lime sauce.