To prepare the shrimp, Place the juice of 2 limes, salt, pepper and cumin powder in a zip lock bag, add the shrimp and marinade in the refrigerator for 15 minutes.
In a large skillet heat the oil over medium-high heat. Add the shrimp and cook until the shrimp are pink and cooked through, about 2 minutes each side.
Remove from the heat and let them cool. Reserve 8 shrimp for garnish and cut the rest into pieces at 3 pieces per shrimp.
In a large bowl mix the pineapple chunks, red onion, cilantro, shrimp, juice of 1 lime, salt and pepper. Mix all the ingredients well, add the avocado and fold into the mixture.
Serve in martini glasses and top with 2 whole shrimp each glass.