Prepare the Mushroom & Buckwheat Filling:

1. Heat 1 Tbsp oil in a large non-stick pan over medium heat.
2. Add chopped onion and sauté for 2 minutes, stirring occasionally.
3. Add sliced mushrooms and cook for 4-5 minutes, until soft and browned.
4. Stir in cooked buckwheat, season with salt to taste, and set aside to cool.

Make the Kotlety:

1. In a large mixing bowl (or stand mixer with paddle attachment), combine:

   • Ground turkey, ground beef, grated onion (with juice), garlic, zucchini, egg, salt, pepper, mayonnaise, and 1 Tbsp flour.
   • Mix until well combined.

2. Set up an assembly line:

   • Bowl of cold water (to keep hands wet and prevent sticking).
   • Bowl of meat mixture.
   • Bowl of mushroom/buckwheat filling.
   • Shallow bowl with flour for dredging.

3. Form the Kotlety:

   • With wet hands, take a flat ice cream scoop of meat mixture.
   • Create a well in the center and fill with 1-1½ tsp mushroom-buckwheat filling.
   • Seal the edges around the filling, ensuring no gaps.
   • Shape into an oval patty.

4. Dredge in flour:

   • Lightly coat each kotleta in flour, patting off excess.
   • Place on a floured plate until ready to cook.

Cook the Kotlety:

1. Heat 2 Tbsp oil in a large non-stick pan over medium heat.
2. Add kotlety (about 5 at a time), cover, and sauté for 4 minutes without disturbing.
3. Remove cover, flip, and cook for another 3 minutes.
4. Turn onto sides for 1 additional minute to brown evenly.
5. Transfer to a plate and cover to keep warm while cooking the rest.
6. Wipe the pan with a paper towel between batches, adding more oil as needed.