Add the sliced steak to a large bowl. Sprinkle over a couple of good pinches of salt and black pepper, then sprinkle the flour over top. Toss everything together to coat the meat well, making sure each piece is evenly covered.

Place a large heavy-bottom skillet or cast-iron pan (12 inches or wider) over medium-high heat and add 2 to 3 tablespoons of avocado oil. Once the oil is hot and shimmering, add the beef in batches and sear quickly for about 2 minutes until browned on the outside but still rare on the inside. Don't overcrowd the pan. Remove the seared beef to a clean plate and repeat with remaining batches.

Add a touch more oil to the same pan, then add the sliced onions and sauté for about 10 minutes until softened and golden-brown. You'll notice them becoming caramelized at the edges. Add another pinch of salt and black pepper, plus the Italian seasoning, paprika, smoked paprika, and white pepper. Stir to combine and cook for about 30 seconds until fragrant.

Add the sliced bell peppers to the pan with the onions and sauté for 2 to 3 minutes until they soften yet still maintain a slight crispness. Add the minced garlic and stir just until fragrant, about 30 seconds.

Stir in the tomato paste and cook for about 30 seconds to remove the raw flavor. Then stir in the beef stock or broth to create the sauce. Check the seasoning and add additional salt and pepper if needed. The sauce should taste well-balanced with savory depth.

Add the seared steak back into the pan and stir to combine. Simmer for just 30 seconds to 1 minute to warm the steak through and allow the sauce to coat every piece.

Serve the pepper steak over white rice or your favorite side dish. Garnish with chopped fresh green onions or parsley for brightness and freshness.