In a large skillet, heat olive oil on medium heat. Cook onions and leeks until translucent, about 5 to 7 minutes. Add mushrooms, garlic, salt, and pepper. Stir frequently until mixture is cooked through, about 15 to 20 minutes.

Place a crêpe cooked side up on a clean surface. Place 3 to 4 tablespoons of the mushroom filling towards the bottom of the crêpe. Fold the lower edge of the crêpe over the filling, fold the sides inwards, and roll up over the filling, tucking the edges in as you roll. Repeat with the remaining crêpes and filling.

Once the blintzes are assembled, heat the oil in a skillet over medium heat until hot. Carefully place 3 to 4 blintzes seam side down and fry for 1½ to 2 minutes on each side, until they are golden brown.

 Serve warm, garnished with chopped cilantro.