In a bowl, whisk together the garlic powder, chili powder, paprika, oregano, salt and pepper. Pat the shrimp dry with a paper towel and place it in a ziplock bag or a baking dish. Drizzle 2 tablespoons of oil on the shrimp and toss. Place the peppers and onions in a separate bag or dish and drizzle them with the remaining oil. Divide the seasoning mix evenly between the shrimp and peppers - cover each with half of the seasoning and toss well. Stick both in the fridge to marinate for 30 minutes.
When you're ready to cook, heat a large nonstick skillet or pan over medium-high heat. I don't add any extra oil because there is often some residual from marinating, but add some if you feel you need it! Add the shrimp first (in one layer, so you might have to do it in batches) and cook until pink and opaque. Remove the shrimp and set it aside on a plate. Add the peppers and onions and cook them until softened and almost charred, about 5 to 6 minutes. Turn off the heat.
Add the shrimp back into the peppers and it's ready! Serve with your tortillas of choice (I like to use corn here), crumbled queso fresco cheese, avocado, fresh cilantro and a spritz of lime. THE BEST!