Remove the minute steaks from the refrigerator and let them rest for 5-10 minutes to reach room temperature. Preheat the oven to 100°C (212°F) on fan-assisted mode.
Slice the onion. Fry the sliced onion in roughly 1 teaspoon butter over medium heat for 3-4 minutes until golden yellow. Transfer to a container and keep warm.
While the onions are frying, wash the lettuce and slice the tomato.
Place the bread in the preheated oven to warm for 3-4 minutes while you cook the meat.
Heat roughly 1 teaspoon oil in a frying pan over medium-high heat. Fry the minute steaks for 1-2 minutes on each side until browned and cooked through. Just before removing from heat, add the garlic butter to the pan and spoon it over the steaks. Season with salt and pepper on both sides. Set the pan aside for 1-2 minutes so the meat can rest and the juices redistribute.
While the steaks rest, remove the bread from the oven. Spread the green pesto on one side of the bread. Layer the tomato slices and lettuce on top. Spread the sour cream on top. If desired, add the BBQ sauce.
Place the cooked steaks on the lettuce and tomato layer. Top with the warm sautéed onions. Pour the pan juices over the meat.