Season the venison steaks and rub them with oil.
Heat a griddle or frying pan. When hot, add the venison and cook for a minute on each side - add the orange juice and zest, turn down the heat, and cook for another 2-5 minutes on each side (depending on the thickness of the steak and how well-done you like it) . When the steaks are cooked to your liking, transfer them to a plate, cover and rest.
Steam the spinach/ cavolo nero and set aside.
Toast the bread slices or cut the rolls in half. Spread the paté on the base ( quite thickly) of your sandwich.
Cut the venison into thin slices and lay them on top the paté. Add the veggies or salad leaves.
Spread some onion marmalade on the other piece of bread and close the sandwich.
Cut in in half and enjoy.