Slice liver and hearts lengthwise into strips ½-in/1cm thick. Cut kidneys into 1-in/2.5cm cubes. Wash and pat dry.
In a large skillet, heat the oil over medium-high heat and add the liver, hearts, and kidneys. Sauté for 2 minutes. Add the onions and garlic and sauté for 3 to 5 minutes until brown. Add tomato paste, flour, salt, and pepper and stir-fry for 1 min