Place orange juice, hot pepper flakes, garlic, salt and pepper in a medium saucepan. Bring to a boil; reduce heat to a very gentle simmer. Meanwhile, peel shrimp, leaving tails attached. Immerse shrimp in orange juice mixture and poach for 3 to 4 min. or until shrimp are just opaque. Do not overcook.
Use a slotted spoon to remove shrimp, and drain on a paper-towel-lined plate. Refrigerate. Reserve 3 tbsp (45 mL) of poaching liquid, removing garlic pieces, and cool.
Combine avocado with cooled poaching liquid, red onion and cilantro; season with additional salt and pepper to taste. Divide avocado mixture and shrimp among four plates or glasses and serve.