In a small bowl, mix together the chili powder, cumin, paprika, onion powder, salt, and pepper.
Place the shrimp in a large bowl and add 2 tbsp oil. Stir to coat the shrimp. Add the seasonings and toss to fully coat.
Heat the remaining 2 tbsp of the oil in a large skillet over medium heat. Add the bell peppers and onion and sauté, stirring often, until softened and lightly charred, about 15 minutes. Transfer to a bowl.
In the same skillet, add the shrimp and cook, stirring often, until no longer pink and cooked through, about 5 to 7 minutes. Set aside.
Heat a fajita skillet over high heat for about 3 to 5 minutes. Carefully add the onions/peppers to the fajita skillet and then top with the cooked shrimp. Or, mix the sautéed onions/peppers with the shrimp in the skillet you cooked the onions and shrimp in.
Heat the tortillas over a gas flame, on your grill, or in the microwave.
Garnish with chopped cilantro and a squeeze of fresh lime. Serve at once with all the fixings at the table.
