Heat oil in a large cast iron pan or skillet on medium heat.Add onions, pepper, jalapeno, and garlic and saute until tender, about 10 minutes.Increase the heat to high and add ground beef and taco seasoning and stir to combine and brown the meat. Add the tomato sauce and let simmer for 1 minute. Sprinkle in flour and incorporate fully.Reduce heat to medium and add in milk and cook until the mixture starts bubbling, about 2 minutes.Remove from heat and fold in ¼ cup of the fried jalapeños and cheese until cheese is fully melted. Top with remaining jalapeños and serve hot with tortilla chips.