For the ox steak with zucchini vegetables, preheat the gas grill on maximum setting for approx. 30 minutes (300 °C).
Chop the zucchini, bell bell pepper and onion and sauté briefly in a frying pan. Season with salt and a dash of soy sauce. Leave to stand.
For the sauce, whisk the sour cream until smooth, stir in the pressed garlic and chives, and season with mayonnaise and salt. Put in a cold place. Bake the Rösti in the oven at 200 °C for about 20 minutes until golden brown.
About 10 minutes before the Rösti are ready, remove the meat from the refrigerator and pat dry with a sheet of kitchen roll. (Do not salt!) Sear on the preheated grill for approx. 4 minutes. Attention: be sure to turn every 60 seconds!
Remove meat from grill and let rest in a preheated, lukewarm pan for 5 minutes. Sprinkle the steaks with a pinch of crunchy salt flakes and serve together with the vegetables, the Röstis and the chive sauce.