Evenly season steaks with pepper and Cajun seasoning. Heat oil in a cast iron skillet over medium-high heat; add steaks and brown well on both sides. Remove from the pan and drain on paper towels. Add onions and bell pepper to pan drippings; sauté until softened, about 10 minutes. Add garlic, sauté until fragrant, about three minutes. Deglaze with beef stock, add steaks back to pan, return to a simmer. Cover with lid, reduce heat to low, and cook 1½ to 2 hours or until fork tender, stirring often. Serve over hot cooked rice or biscuits.