For the tacos: in a bowl, toss the shrimp with the garlic, cumin, chili powder, salt and pepper. Let the shrimp marinate while you prepare the salsa. Warm the oil in a large skillet over medium heat. Cook the shrimp, turning occasionally until pink and opaque, about 5 minutes. Remove from heat and serve immediately. Place 3-4 shrimp into a tortilla, top with pineapple salsa and a squeeze of lime.