Preheat grill or cast-iron grill pan to medium-high heat (400-450 degrees Fahrenheit).
Pat steak dry with paper towels and season both sides with 1 tablespoon olive oil, salt, and pepper.
Toss zucchini rounds with remaining olive oil and a pinch of salt.
Grill the steak for 4 to 5 minutes per side for medium-rare, or until internal temperature reaches 135 degrees Fahrenheit.
Place zucchini rounds on the grill and cook for 3 minutes per side until char marks appear and texture is tender-crisp.
Remove steak from heat and let rest on a cutting board for 7 minutes to retain juices.
In a small mixing bowl, whisk together Greek yogurt, lemon juice, minced garlic, and chives until smooth.
Slice the rested steak against the grain into thin strips.
Assemble bowls by layering 1 cup of grains, half the grilled zucchini, and half the steak slices.
Top with a generous dollop of the creamy garlic sauce and serve.