STEP ONEWHISK together oil, vinegar, oregano, parsley, flour and garlic powder in medium bowl. Season to taste with salt and pepper. Set aside.
STEP TWOHEAT 1/4 cup oil over medium heat in large skillet. Add peppers, onions and garlic. Sauté 1 minute. Add shrimp and marinade. Cook 10 minutes. Serve with warm flour tortillas, lettuce, tomatoes, cheese, avocados and sour cream.
OPTIONAL GRILLING METHOD
STEP ONEDOUBLE marinade recipe and prepare. Add shrimp and vegetables to marinade; cover and refrigerate. Soak 1 dozen wooden skewers in water for at least 30 minutes.
STEP TWOPREPARE gas or charcoal grill. Heat to medium heat.
STEP THREEREMOVE shrimp and vegetables from marinade; discard marinade. Skewer shrimp onto 4 prepared wooden skewers. Skewer vegetables onto remaining 8 skewers. Grill until vegetables are tender and shrimp are cooked through.