Toss shrimp with Relajo, kosher salt, and 1 Tbsp. oil in a medium bowl. Heat remaining 3 Tbsp. oil in a large skillet over medium-high. Cook shrimp in a single layer, undisturbed, until crisp and browned underneath, about 2 minutes. Turn over and cook until crisp on the other side, about 1 minute. Immediately add garlic and cook, shaking pan often, until garlic is just golden, about 1 minute.