Put the tomatoes in a large bowl and sprinkle with 1/2 teaspoon salt and a few grinds of pepper; set aside until juicy, about 20 minutes.
Meanwhile, cook the bacon in a large skillet over medium heat until crisp, about 4 minutes per side. Transfer to a paper towel-lined plate and let cool slightly, then crumble into bite-size pieces.
Pit and peel the avocado; cut into 1/2-inch pieces and toss with the lemon juice in a large bowl. Add the tomatoes and gently toss. Drizzle with the dressing and top with the bacon, chives and blue cheese.
Blue Cheese Dressing
Puree 1/2 cup each crumbled blue cheese and sour cream, 1/3 cup buttermilk, 1 small garlic clove (smashed) and 1 tablespoon white wine vinegar in a blender. Transfer to a bowl and stir in 1/4 cup more blue cheese, 2 to 3 dashes Worcestershire sauce and/or hot sauce, and 1 tablespoon chopped parsley. Season with salt and pepper. (Makes about 2 cups.)