In a large bowl, combine the shrimp, olive oil, Cajun seasoning, garlic powder, onion powder, smoked paprika, salt, black pepper, and red pepper flakes. Toss to coat the shrimp evenly and let marinate for 15-20 minutes.
Heat a large skillet over medium-high heat. Add the marinated shrimp and cook for 2-3 minutes on one side until they turn pink.
Flip the shrimp and add the sliced bell pepper, onion, and minced garlic to the skillet. Cook for an additional 3-4 minutes, stirring occasionally, until the vegetables are tender and the shrimp are fully cooked.
Remove from heat and garnish with chopped parsley. Serve immediately with lemon wedges on the side.