1. Heat oven to 350 degree F. In a large bowl, combine shrimp, 1 tablespoon each oil and lime juice, garlic, 1/4 teaspoon salt, 1/8 teaspoon pepper, cumin, and chili powder. Stir to coat shrimp.
2. Heat remaining oil in a large nonstick skillet over medium-high heat and cook onions until translucent, 5 minutes. Add peppers, remaining salt and pepper, stirring frequently, 5 minutes more. Stir in 2 tablespoons cilantro. Transfer to an ovenproof bowl and keep warm in oven.
3. Heat skillet over medium heat and add shrimp. Saute until just cooked through, 3 to 5 minutes. Stir in remaining lime juice and cilantro. To serve, wrap each tortilla around vegetables and shrimp. Serve with sour cream and salsa, if desired. Makes 4 to 6 servings.