Peel shrimp and devein. Set aside. In bowl combine lemon juice, 1/4 cup olive oil, minced garlic, and red pepper flakes. Add shrimp and stir to coat. Let sit for 20 minutes. Meanwhile, in separate bowl combine pineapple, tomato, and onion and parsley. Drizzle on remaining oil and mix together. Remove shrimp from marinade and grill, broil or cook in cast iron pan until shrimp are pink. Plate and top with salsa.