Simmer soy sauce, honey, ginger, vinegar and garlic in a small saucepan until a glaze forms (1-2 minutes), then set aside.
Heat oil in a frying pan over medium-high heat, add beef and brown on all sides (2-3 minutes). Remove from heat, pat dry with paper towels, brush generously with soy glaze (you won’t use all of it), then place in freezer to chill (8-10 minutes).
For the soba, cook soba according to packet instructions until al dente, adding peas in the last minute, then rinse under cold running water. Drain well, then combine in a bowl with vinegar, soy sauce, sesame oil, cucumber and spring onion. Toss to combine, then divide among bowls.
To serve, thinly slice beef, pile on top of noodles and scatter with spring onion, sesame seeds and any remaining soy glaze to taste.