To make the marinade: Place onions in a large ceramic bowl and crush with the bottom of a glass until juice is rendered and onions look translucent. Stir in garlic, olive oil, lemon juice, oregano, black pepper, turmeric, curry powder, and salt. Add beef and toss to coat. Cover the bowl with plastic wrap and marinate in the refrigerator, 8 hours to overnight.

To make the sauce: Combine sour cream, olive oil, lemon juice, salt, black pepper, dill, and garlic in a medium bowl; mix until well combined. Cover the bowl with plastic wrap and refrigerate for 8 hours to overnight.

Preheat the oven’s broiler and set the oven rack about 6 inches from the heat source.

Remove meat from marinade, brushing off extra onions; discard marinade. Spread meat on a baking sheet without overlapping. Season with salt.

Cook under the preheated broiler until meat is browned and crispy, about 3 minutes per side, turning halfway through cooking.

Divide meat between pita breads and drizzle with tzatziki sauce to serve. You can use chicken instead of beef, too.