Preheat the grill to medium-high heat.

In a small bowl, mix together the olive oil, garlic powder, onion powder, smoked paprika, salt, and pepper.

Rub the mixture all over the flank steak.

Place the steak on the grill and cook for about 4-5 minutes on each side for medium-rare, or until desired doneness.

During the last few minutes of grilling, add the zucchini slices to the grill and cook until tender and slightly charred, about 3-4 minutes.

Remove the steak and zucchini from the grill and let the steak rest for 5 minutes before slicing it thinly against the grain.

In a small bowl, combine the sour cream, mayonnaise, lime juice, and cilantro to make the creamy sauce.

To assemble the bowls, divide the cooked brown rice among four bowls. Top with sliced steak, grilled zucchini, cherry tomatoes, and avocado. Drizzle with the creamy sauce before serving.