In a saute pan, over medium heat, add the olive oil. When the oil is hot, add the onions and saute for 1 minute. Add the duck confit and saute for 1 minute. Season with salt and pepper. Stir in the tamarind sauce and saute for 2 minutes. Season with salt and pepper. Stir in the green onions and remove from the heat. In a large skillet, heat the vegetable oil for frying. When the oil is hot, fry the tortillas, a couple at a time, until golden brown, about 2 minutes. Remove the tortillas from the oil and drain on a paper-lined plate. Season the tortillas with salt and pepper. In a small mixing bowl, whisk the sour cream, lemon juice and cilantro together. Season with salt and pepper. In another small bowl, combine the avocados, lime juice, garlic and 2 tablespoons tomatoes, together. Season the mixture with salt and pepper. To assemble, lay one tortilla in the center of each plate. Place 1/2 cup of the duck mixture on top of each tortilla. Top the duck meat with the shredded lettuce, tomatoes and cheese. Top with a second tortilla and repeat the latter procedure. Top each taco with the remaining tortillas. Garnish the tacos with the cilantro sour cream and guacamole.