Marinate the beef:

In a large bowl, combine olive oil, lemon juice, garlic, oregano, thyme, salt, and pepper.

Add the thinly sliced beef and toss to coat.

Cover and refrigerate for 2-4 hours, or overnight.

Make the tzatziki:

In a small bowl, combine Greek yogurt, grated cucumber, minced garlic, chopped dill, olive oil, lemon juice, salt, and pepper.

Stir to combine and refrigerate until ready to serve.

Cook the beef:

Thread the marinated beef onto skewers.

Grill or cook the skewers over medium-high heat for 15-20 minutes, or until cooked through and slightly charred.

Assemble the gyros:

Slice the pita bread open.

Fill with chopped lettuce, tomatoes, red onion, and cooked beef.

Drizzle with tzatziki sauce.

Enjoy your delicious beef gyros!

Optional toppings: You can also add other toppings to your gyros, such as hummus, feta cheese, or pickled red onions.