In a small bowl whisk together 2 tablespoons lime juice, 3 tablespoons olive oil, 2 teaspoons minced garlic, 2 teaspoons chili powder, 1/2 teaspoon ground cumin, 1/4 teaspoon paprika, 1/2 teaspoon salt, 1/4 teaspoon ground black pepper, and 1/4 teaspoon red pepper flakes.: The aroma will be bright and fragrant, with citrus on top and warm spices beneath, and you should notice the oil catching the light as you whisk. This emulsified mixture coats the shrimp evenly so they grill with a uniform crust, and whisking helps dissolve the salt for consistent seasoning. If your spices clump, use the back of a spoon to break them up, because uneven distribution causes spots of over salty or over spicy bites. Avoid using bottled citrus here, fresh lime juice gives a lively acidity that bottled juice lacks.
Pour into a large ziplock bag and add the shrimp. Close the bag and toss to coat. Refrigerate for 30 minutes - 1 hour to marinate the shrimp.: As the shrimp bathes in the marinade you will smell garlic and citrus seeping into the flesh, and the surface will glisten when thoroughly coated. Marinating briefly allows flavors to penetrate without making the texture mushy; the acid is light enough for this short window. A common misstep is over-marinating, which can make the shrimp mealy, so stick to the stated time. Gently massage the bag occasionally to ensure every piece is covered and refrigerate flat for even chilling.
Preheat the grill to medium heat. Put the shrimp on skewers and place them on the grill. Grill on each side for about two minutes or until cooked and pink throughout.: You want the grill hot enough to create those quick sear marks and sizzling sounds that signal Maillard reaction, but not so hot that the exterior chars before the interior cooks. The shrimp should curl into a loose C shape and turn opaque pink; that visual cue means they are done. If you cook them too long they will feel rubbery, so watch carefully and test one to check doneness. Oil the grates lightly or brush the shrimp so they release easily, and use tongs to flip them once for the best texture.
To make the sauce, add 1 large pitted and diced avocado, 1/2 cup greek yogurt, 1 teaspoon minced garlic, 2 tablespoons lime juice, and 2 tablespoons chopped cilantro to a blender or food processor. Pulse until smooth. Season with salt and pepper to taste. Serve alongside the shrimp as a dipping sauce.: As you blend, the mixture will transform from chunky to luxuriously smooth, and the smell will be herbaceous and bright with garlic and lime. This technique yields a creamy emulsion that clings to the shrimp and doubles as a dip or drizzle, and pulsing first prevents overworking the avocado into a glue like texture. A common error is using an overripe avocado which makes the sauce thin and brown quickly, so aim for ripe but firm fruit. If your blender sticks, scrape down the sides and add a teaspoon of cold water to help it move.
Pulse until smooth Season with salt and pepper to taste Serve alongside the shrimp as a dipping sauce: When the sauce is ready you will notice a silky mouthfeel and a bright green color with flecks of cilantro . Taste and fine tune with a pinch of salt or a squeeze of lime if it needs more lift. Serving it chilled next to hot grilled shrimp provides that delightful contrast, and the creamy texture helps balance the spice. Avoid adding too much salt at once, since you can always adjust at the table, and keep the sauce covered in the fridge if you make it ahead to preserve freshness.