1. Slice the meat into thin pieces or into 1" cubes. Place in a bowl and combine the salt, pepper, oregano, and dried dill. Mix in the olive oil.
2. Heat a cast iron skillet to medium high. Quickly sear the front and back sides of the meat. The pan should be hot enough that you literally cook each side for about 30 seconds. TIP- Don't overcrowd the pan. Do this in small, workable batches to make it easier.
3. Place the seared meat into a slow cooker. Add 1/2 of a juiced lemon, and the red wine (optional). Set it to low for 6-8 hours or high for 4 hours.
4. To make the tzatziki sauce, grate a cucumber over a dish towel or cheese cloth. Once grated, stand over the sink and squeeze the cucumber into the towel to remove as much water as possible. A LOT of water will come out!
5. In a bowl, combine the yogurt or sour cream, the cucumber, lemon juice, fresh dill, garlic, and salt/pepper. Allow the flavors to hang out and develop (still tastes good however if you make right before serving...but it gets better with time).
6. Assemble by filling the keto naan/pita bread with the meat, red onion slices, tomato wedge, a few cucumber slices and top with the tzatziki sauce!