Place the 4 beef steaks (250 g each) in a large plastic bag, add 0.75 cup teriyaki sauce, seal the bag, and shake well to coat. Refrigerate overnight (at least 8 hours).
In a bowl, combine 0.5 cup cucumber, 0.5 cup sour cream, 0.5 cup mayonnaise, 1 tbsp chives, 1 teaspoon dill, and 0.25 teaspoon salt. Cover and refrigerate until serving.
Preheat the grill to medium heat. Remove the steaks from the bag (discard the marinade), place on the grill rack, and cook for 4 to 5 minutes per side until your desired level of doneness.
Serve the grilled steaks with the cucumber sauce and fresh vegetables (optional).