Remove heads and body shells from shrimp but leave on tail shells.
Devein shrimp by removing black spinal cord. Cut each green onion in 4 daisies. Put shrimp, green onions, bell pepper and olives in a bowl. Mix garlic, lemon juice, olive oil, sugar, mustard and horseradish.
Pour over shrimp mixture, cover and marinate at least 2 hours, stirring occasionally. Remove ingredients from marinade and thread equally on 8 wooden picks. Drain on paper towels.
VARIATION: Add small slices avocado to shrimp mixture.