To make the mojo de ajo, in a small saucepan over medium-low heat, combine the garlic, olive oil and the 1/2 teaspoons salt, stir to mix and cook, stirring occasionally, until the mixture is barely simmering. Reduce the heat to very low and cook at a very gentle simmer, stirring occasionally, until the garlic is lightly golden (the color of light brown sugar), about 30 minutes. (The slower the cooking, the sweeter the garlic.).
Add the lime juice and simmer, stirring, until most of the juice has evaporated or has been absorbed into the garlic, about 5 minutes. Stir in the chilies, taste and adjust the seasonings with salt. Keep the pan over low heat so the garlic will be warm when the shrimp are ready.
In a large nonstick fry pan over medium-high heat, spoon 1 1/2 Tbs. of the oil (but not any garlic) from the mojo. Add half the shrimp to the pan, season with salt, and stir gently and continuously until the shrimp are just cooked through, 3 to 4 minutes. Stir in half the cilantro. Scoop the shrimp into a deep serving platter and repeat with another 1 1/2 Tbs. of the oil and the remaining shrimp and cilantro. When all of the shrimp are cooked, use a slotted spoon to scoop out the warm bits of garlic and chilies from the mojo pan and scatter them over the shrimp. Serve immediately with the lime wedges alongside to squeeze over the shrimp. (You may have as much as 1/3 cup of the oil left over. Reserve for another use.) Serves 6.