I have so many wonderful memories of growing up on a farm with a big family. One of the best things about birthdays is that mom let us pick our favorite food for our birthday dinner. Mine of course was liver, and spinach. Strange choice for a child but mom always came through.
Remove any heavy blood vessels and outside membrane from liver if butcher has not previously done it. Slice liver approximately 3/4 inch thick.
Put flour in a large zip lock bag (gallon size). Add liver and shake to coat each slice
In large frying pan, add enough oil to cover the bottom. Heat oil then lay liver in hot oil brown on one side. turn over. Top with sliced onions. Sprinkle with salt and pepper and fajita seasoning. Cover and turn heat to low. Cook about 20 minutes. The secret to good tender liver is slow cooking and not over cooking.
Serve with mashed potatoes and a green salad, or baked potato and side of steamed spinach.