Spread the cleaned shrimp onto a sheet tray. Add the garlic, salt, and olive oil and toss to coat. Transfer to the center rack in the oven and roast until the garlic is very aromatic and the shrimp is pink with red tails, about 15 minutes.
Hot out of the oven, sprinkle immediately with oregano, the juice of 1 lime, and as much or as little cayenne powder as you like. Serve immediately. Adjust salt to taste.
Herbs: You may use 1 tablespoon dried oregano (though fresh is best) or 2 tablespoons of fresh parsley, cilantro, or basil in place of the oregano.Olive Oil: You may replace with unsalted butter which will give you more caramelization. With this consideration, I recommend a shorter roast time. Pull the tray out after 8 minutes. The shrimp should be fully cooked.Lime: When buying limes, look for the fruit to feel heavy compared to its size. You may need 2-3 limes instead of 1 juicy lime, depending on the time of year; some limes contain very little juice. Lemon juice is a good alternative.