For the fillet steak:
1) Season the fillet with salt and pepper to taste and with garlic powder on both sides. Combine the remaining ingredients in a sealable bag. Add the meat to the bag and marinate in the refrigerator for 2 to 4 hours.
2) Preheat the oven to 200C/Gas 6.
3) Remove the fillet from the bag and transfer to a grill pan. Roast in the oven for 12 to 20 minutes, depending on how rare you want the steak. Remove from the oven and allow to rest before slicing.
For the lobster tails:
1) Remove the raw lobster meat from the shell and cut into chunks.
2) In a large frying pan over medium-high heat, melt the butter and saute the onions until softened. Add the lobster meat and cook until it just begins to turn pink.
3) Stir in the lemon juice and cook until it has reduced by half. Then stir in the cream and cook and stir until the cream thickens.
4) Stir in the Parmesan, parsley and salt and pepper, to taste.
For the dish assembly:
1) Build the sandwich starting with some of the sliced fillet mignon on the toasted roll. Spoon some of the lobster chunks on top of the steak. Load on the fries.
2) Top the sandwich with a spoonful of the Parmesan sauce from the lobster. Pile on some lettuce, tomato, onion slices and crispy bacon, if desired. Serve immediately.