In a large bowl, whisk together the Dijon and lemon juice and slowly pour in the olive oil, whisking constantly until thickened. Season generously with salt and pepper to taste.
Add the roast chicken, pecans, onions, and tarragon and stir to combine.
Cut the ends off the two baguettes, and slice each one lengthwise, then cut them into 6-inch pieces (you’ll have some pieces left over…save for breakfast toast). Divide the chicken salad mixture amongst four baguette bottoms, add some lettuce leaves, and top with baguette tops.
Wrap each one in parchment paper and tie with butchers’ twine if you like. Also, feel free to add additional sandwich toppings like mayonannaise, salted butter, sliced tomatoes, sliced cucumbers, or sliced radishes. Enjoy!
NOTE: These are fine to transport to a picnic, but if you’re going to be carrying them around for longer than an hour, bring a cooler or cooler packs.