Rinse shrimp in cold water. Pat dry with a paper towel and set aside on a plate.
To make the marinade:
Whisk together the tomato paste, water and oil in a small bowl. Add garlic, chili powder and oregano. Mix well.
Using a brush, spread the marinade (it will be thick) on both sides of the shrimp. Place in the refrigerator.
Prepare broiler. Lightly coat the broiler pan with cooking spray. (TIME SAVER: foil the pan for easy clean up). Position the cooking rack 4 to 6 inches from the heat.
Put the shrimp on skewers and place under broiler.
Turn the shrimp after 3 to 4 minutes.
The cooking time varies depending on the heat of the fire, so watch carefully.
Serving size depends on the amount of shrimp per skewer. 2 skewers with 6 shrimp each = 8 servings