Pat the steak cubes very dry with paper towels to ensure a good sear.

Toss steak cubes with salt, pepper, and smoked paprika if using.

Preheat a large cast-iron skillet over medium-high to high heat for 2–3 minutes until it's almost smoking.

Add avocado oil, swirling to coat the pan. The oil should shimmer right away.

Sear half the steak cubes in a single layer without crowding the pan for 1–2 minutes per side until browned.

Transfer the seared steak to a plate and repeat with the remaining steak.

Reduce the heat to medium-low and add 3 tablespoons of butter to the pan. Once melted, stir in minced garlic and red pepper flakes, cooking for 20–30 seconds until fragrant.

Return all the steak to the pan, add the remaining tablespoon of butter, and toss for 30–60 seconds until well coated.

Taste and adjust seasoning, adding more salt or pepper if needed, and a squeeze of lemon if desired.

Plate the steak bites immediately to preserve the crust, then spoon extra garlic butter from the pan over the top.