Combine olive oil, minced garlic, lemon juice, dried oregano, thyme, salt, and black pepper in a bowl. Whisk until well blended. Coat the sirloin steak thoroughly with the marinade and let it marinate in the refrigerator for at least 30 minutes.

Prepare tzatziki by mixing Greek yogurt, grated cucumber, minced garlic, lemon juice, salt, and olive oil. Stir until well combined and refrigerate.

Heat skillet over medium-high heat, add a splash of olive oil. Sear marinated sirloin steak for 4-5 minutes per side for medium-rare. Remove and let it rest for 5 minutes before slicing.

Assemble the bowl by layering cooked grains, sliced steak, fresh toppings, tzatziki, and drizzle with lemon vinaigrette.