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

In a mixing bowl, whisk together the sour cream or Greek yogurt, Dijon mustard, fresh herbs, garlic powder, salt, and pepper until smooth. Refrigerate for at least 10 minutes.

Slice the zucchini into half-inch rounds, drizzle with olive oil, and season with salt and pepper. Grill for 2-3 minutes on each side.

Heat olive oil in a grill pan over medium-high heat. Cook the steak for 3-4 minutes on each side until medium-rare, then let rest for 5-10 minutes.

Assemble the bowl with a base of rice or mashed potatoes, top with sliced steak and grilled zucchini, and drizzle with creamy herb sauce.