Put the bacon in a small saucepan over medium heat and cook, stirring often so the bacon doesn't burn, until the fat begins to render. Add the shallots and cook until softened, about 3 minutes. Remove the pan from the heat and whisk in the sherry vinegar and mustard, followed by the olive oil and tarragon. Season as needed with salt and pepper.
Pour the vinaigrette over the greens in a bowl and toss. Add the goat cheese and toss again. Serve immediately.