Mix marinade ingredients together in a bowl before coating the sirloin steak thoroughly with it. Allow the steak to marinate in the refrigerator for anywhere from 30 minutes up to 4 hours.
In another bowl, combine all the tzatziki ingredients: Greek yogurt, grated cucumber, lemon juice, minced garlic, fresh dill along with salt and pepper to taste before chilling it in the fridge until ready to serve.
Whisk together all vinaigrette ingredients including olive oil, lemon juice, honey if using, minced garlic and dried oregano until well combined.
Sear your marinated steak in a hot skillet over medium-high heat cooking each side for about 4–5 minutes until it's beautifully browned on both sides while remaining tender inside; allow it to rest before slicing thinly against the grain.
Assemble your Mediterranean Steak Bowl by layering cooked grains at the bottom followed by sliced steak then topping with cherry tomatoes, diced cucumber, red onion slices alongside olives and feta cheese if using; drizzle generously with tzatziki sauce and vinaigrette before serving straight away!