Beef Teriyaki with Sesame Cucumber Salad Recipe

2x 150g premium grade beef sirloin fillet, trimmed
80ml Japanese soy sauce
40ml mirin
30ml cooking sake
1 clove garlic, minced
1 tsp ginger, minced
1 tbsp raw sugar
20ml vegetable oil
1 oriental cucumber, finely diced
2 tbsp daikon, finely diced
watercress leaves
2 tsp caster sugar
20ml rice vinegar
1/2 tsp sesame oil
1 tbsp white sesame seeds, roasted