Season steaks on both sides with salt, black pepper, and 1 teaspoon of Cajun seasoning.
Heat olive oil in a cast-iron skillet over medium-high heat until shimmering.
Sear steaks for approximately 4-5 minutes per side for medium-rare internal temperature (135°F/57°C).
Remove steaks from the skillet and transfer to a warm plate to rest.
Reduce skillet heat to medium and add butter, scraping the bottom of the pan to release fond.
Sauté minced garlic and diced bell peppers for 2 minutes until softened.
Add shrimp and the remaining Cajun seasoning to the skillet, cooking for 3 minutes until shrimp are pink and opaque.
Pour in heavy cream and simmer for 2-3 minutes until slightly reduced.
Whisk in Parmesan cheese until the sauce is smooth and thickened.
Plate the rested steaks and spoon the Cajun shrimp sauce generously over the top.
Garnish with chopped fresh parsley.