Place olive oil in 12-inch nonstick pan, turn heat to medium high and cook until bubbly but do not color. Add the garlic and cook for 30 seconds. Add the lemon juice, pepper flakes, celery, and scallops. Cook for 1 minute. Add the shrimp and squid. Cook until shrimp is pink in color and seafood is cooked through, about 5 minutes. Add parsley. Season with salt and pepper, to taste. Serve immediately.