Heat sizzling platter or an oven safe skillet in the oven until ready to serve.
Remove heads and peel shells of shrimps. Using a small knife, make a shallow cut on the back of shrimps and devein. Wash under cold running water and drain well.
In a bowl, combine chili powder, cayenne pepper, cumin, oregano, garlic powder, onion powder, brown sugar, and salt. Whisk together until well-combined. Add the shrimp and 1 tablespoon of the olive oil. Massage mixture onto shrimp to fully coat. Marinate for about 10 to 15 minutes.
In a thick-bottomed skillet over medium-high heat, heat 1 tablespoon of the olive oil. Add bell peppers and onions, and cook, stirring frequently, for about 2 to 4 minutes or until tender yet crisp. With a slotted spoon, remove from pan and keep warm.
Add the remaining 1 tablespoon olive oil to the pan. Add shrimps in a single layer and cook for about 1 to 2 minutes, turn, and cook for another 1 to 2 minutes. Return bell pepper and onion mixture to pan. Continue to cook, stirring regularly, for about 2 to 3 minutes or until shrimp are cooked (DO NOT overcook as they will turn rubbery!) and vegetables are heated through. Carefully transfer fajitas onto heated sizzling platter.
Serve with flour tortillas, sour cream, and lime wedges if desired.