Pulse the onion and garlic in a food processor until finely minced. Squeeze out the excess liquid.
Add the beef, onion mixture, and seasonings to the food processor. Process until smooth and paste-like. If needed, knead the mixture by hand for 3–5 minutes until sticky.
Press the mixture firmly into a loaf pan. Place the loaf pan inside a larger baking dish and pour about 1 inch of hot water into the outer dish.
Bake at 325°F for 60–75 minutes, or until the internal temperature reaches 165°F.
Drain the fat, cool for 20 minutes, wrap tightly, and refrigerate overnight.
Slice the chilled meat as thinly as possible.
Heat a little olive oil in a skillet and cook the slices for 1–2 minutes per side until browned and crispy.
Serve on warm homemade naan or pita with tzatziki, hummus, cucumbers, tomatoes, and red onion.