Season steak with salt and pepper. In a small bowl, mix 2 Tbsp. of the Merken and 2 Tbsp. of the lime juice with the orange juice, vinegar and oil. Place steak and marinade in a zip top bag, seal, shake to coat steak, and refrigerate for 30 min.
Mash avocado with remaining ½ Tbsp. lime juice, season with salt and pepper, fold in tomatoes, cover and refrigerate.
Preheat oven to 250 degrees. Heat grill to medium high. Remove steak from marinade, pat dry and season with remaining ½ Tbsp. Merken. Mix butter with granulated garlic, season with salt and pepper, and use to butter inside of each piece of bread. Place buttered side up on a baking sheet and toast in the oven until golden, about 20 min. Meanwhile, cook steak on grill to desire doneness. Remove and let rest 5 min. Slice across the grain into ½-inch strips.
Place a layer of avocado mixture on inside of each bottom piece of toasted bread, top with a layer of steak strips and then a layer of green beans. Spread Merken dipping sauce on inside of each top piece of toasted bread, place on top of the green beans and serve.