Pat the steak dry with paper towels, season generously with salt, pepper, garlic powder, and optional onion powder. Let sit at room temperature for 15-20 minutes.

In a mixing bowl, whisk together sour cream or Greek yogurt with Dijon mustard, garlic powder, and a pinch of salt and pepper. Stir in chopped fresh herbs. Cover and refrigerate for at least 10 minutes.

Slice zucchini into thick rounds, coat with olive oil, salt, and pepper. Preheat grill and grill zucchini for 2-3 minutes per side until tender with char marks.

Heat grill pan over medium-high heat, oil lightly and cook seasoned steak for 3-4 minutes on each side for medium-rare. Let rest for 5-10 minutes.

Assemble by layering rice or mashed potatoes, adding grilled zucchini, then slicing steak against the grain. Drizzle with creamy herb sauce.