1. In a blender or food processor, whirl lemon juice, oil, onion, cilantro, garlic, ginger, and chilies until smooth.
2. Mix 1/3 cup chili mixture with yogurt.
3. In a bowl, mix the remaining chili mixture with shrimp and let stand at least 10 or up to 30 minutes, then thread shrimp onto metal skewers.
4. Prepare barbecue for direct heat.
If using charcoal briquets, cover firegrate with a single, solid layer of ignited coals; let them burn down to desired heat. Set grill in place and measure heat.
If using a gas barbecue, turn all burners to high and close lid for 10 minutes. Adjust burners to desired heat. Set grill in place and measure heat.
When grill is hot (you can hold your hand at grill level only 2 to 3 seconds) lay skewered shrimp on it. Turn to cook shrimp evenly until they are opaque but still moist-looking in thickest part (cut to test), 5 to 8 minutes
5. Push shrimp off skewers and serve with yogurt sauce and salt to taste.