In small bowl, stir margarita mix and lime peel. Reserve 2 tablespoons mixture. Add shrimp to remaining mixture; toss to coat. Cover and refrigerate 30 minutes.
In 10-inch nonstick skillet, melt butter over medium-high heat. Cook green and red bell peppers in butter 2 to 4 minutes, stirring occasionally, until crisp-tender.
Remove shrimp from marinade; discard marinade. Stir shrimp into mixture in skillet. Cook 1 to 2 minutes, stirring occasionally, until shrimp are pink and firm. Stir in reserved 2 tablespoons sauce and the cilantro. Cook until heated through.
Meanwhile, cook rice in water as directed on package. Serve stir-fry over rice.