ADD the bacon strips to a large, heavy-bottomed skillet over medium heat. Stir the bacon and cook until crispy. Use a slotted spoon to transfer the bacon to a paper towel lined plate. Pour all but about 2 teaspoons of the bacon drippings out of the pan.
RETURN the pan to the burner over medium heat and add the onions to the pan with a pinch of salt. Stirring frequently, cook until the onions are crisp tender (about 5 minutes) and golden in color. Transfer the onions to a large mixing bowl.
POUR the lemon juice over the two halves of avocado. Coarsely chop the avocado and add to the bowl with the onions. Stir to combine. Add the red wine vinegar, garlic, and all but 2 tablespoons each of the crispy bacon, snipped basil and the bleu cheese and stir well again.
BRING a gallon of water to a full rolling boil in a large stockpot. Salt the water and pour in the pasta. Cook to al dente according to package directions.
DRAIN the pasta, reserving about a cup of the pasta water. Add the hot pasta to the avocado mixture. Stir in gently but thoroughly to distribute the sauce. If it is too thick, add a splash of the reserved pasta water to thin it. Taste and adjust seasonings with salt and black pepper. Top the pasta with the reserved basil, bacon and bleu cheese and serve warm or room temperature.