Combine olive oil, garlic, lemon juice, oregano, thyme, salt, and pepper in a shallow dish; massage into the steak and let marinate for 30 minutes or up to 4 hours.
Heat a cast-iron skillet over medium-high heat; sear steak 4–5 minutes per side for medium-rare; rest 5 minutes before slicing thinly against the grain.
Whisk Greek yogurt, grated cucumber, lemon juice, garlic, dill, salt, and pepper in a bowl; chill until ready to serve.
Whisk olive oil, lemon juice, honey, garlic, oregano, salt, and pepper in another bowl until emulsified.
Cook or reheat grains according to package instructions; dice vegetables and chop herbs while grains warm.
Divide grains among bowls; top with sliced steak, vegetables, olives, and chickpeas; drizzle vinaigrette and add a dollop of tzatziki.