Heat the olive oil in a large skillet over medium heat. Add the onions and cook, stirring, for 1 minute. Add the duck confit and cook for 1 minute. Season with salt and pepper. Stir in the tamarind sauce and cook, stirring, 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. Season the mixture with salt and pepper.

To assemble, lay one tortilla in the center of each plate. Place 1/4 cup of the monterey jack on top of each tortilla, top the cheese with 1/2 cup of the duck mixture. Top the duck meat with the shredded lettuce, tomatoes and avocado.  Garnish the tacos with the cilantro sour cream.