Heat oven to 375°F. In medium bowl, combine sour cream, cucumber and 2 tablespoons of the taco seasoning mix; mix well. In small bowl, combine avocados and lime juice; toss to coat. Set aside.
In another medium bowl, combine shrimp and remaining taco seasoning mix; toss to coat.
Heat taco shells at 375°F. as directed on package.
Meanwhile, heat oil in large skillet over medium-high heat until hot. Add shrimp; cook 3 to 5 minutes or until shrimp turn pink, stirring frequently.
Spoon shrimp into warm taco shells. Top each with sour cream mixture, avocados, salsa and cilantro.