Bake the potatoes. Preheat the oven to 425°F. Line a baking pan with parchment paper. Rub the potatoes with olive oil and sprinkle them generously with sea salt.
Place the potatoes on the prepared pan without poking holes in them. Bake for 50–60 minutes, or until they are tender when pierced with a fork.
Prepare the steak. While the potatoes bake, trim away excess fat and silver skin from the steak. Cut it into roughly 2-inch pieces.
Drizzle the steak bites with 2 tablespoons of avocado oil, then coat them generously with Cajun seasoning.
Heat the remaining 2 tablespoons of avocado oil in a cast-iron skillet over medium-high heat.
Add the steak bites in a single layer. Cook undisturbed for about 2 minutes, or until deeply golden on the first side. Flip once and cook for another minute.
Reduce the heat to low and continue cooking for about 1 minute, adjusting the cooking time according to your preferred doneness.
Push the steak to one side of the skillet. Add 2 tablespoons of butter and 1 tablespoon of minced garlic. Cook until fragrant.
Toss the steak bites through the garlic butter so they are well coated. Cook for another minute, then transfer the steak to a bowl and loosely cover with foil.
Make the Parmesan cream sauce. Using the same skillet, add the remaining 2 tablespoons of butter and remaining minced garlic. Cook until fragrant.
Slowly whisk in the heavy cream. Bring the mixture to a gentle simmer and cook for 3–5 minutes, stirring occasionally, until slightly reduced.
Add the red pepper flakes and Parmesan cheese. Whisk until the cheese melts and the sauce thickens. Taste and adjust the salt and black pepper.
Remove the sauce from the heat. Stir in the fresh parsley and lemon juice.
Assemble. Carefully lift each baked potato and gently drop it back onto the pan from about 12 inches high to help loosen the fluffy interior.
Cut each potato down the center and gently fluff the inside with a fork. Spread some of the remaining butter inside each potato.
Divide the steak bites evenly between the potatoes. Spoon the Parmesan cream sauce generously over each one and serve immediately.