Heat a 10-inch skillet over medium-high heat and add 1 tablespoon of butter.
Season the steak with salt and pepper on all sides, and cook the steak pieces in the skillet in an even layer, undisturbed, for 2 to 4 minutes, to get a good sear on the steak. Stir and brown each side, being careful not to overcook. Remove the steak bites to a plate to keep warm.
In the same skillet, add the remaining 1 tablespoon of butter. Toss in the bell pepper and cook for about 2 minutes, until the bell pepper is lightly browned. Add the garlic and cook until fragrant, about 30 seconds.
Return the steak to the skillet and toss to coat. Garnish with freshly chopped parsley, if desired, and serve.