To make the pickled carrots: Stir the carrots, vinegar, sugar, and salt to blend in a small bowl. Let stand until the carrots soften, at least 1 hour.
To make the spicy mayo: Stir the mayonnaise and Sriracha to blend in a small bowl. (Carrots and mayo can be made up to 4 days ahead. Cover and refrigerate separately.)
To make the sandwiches: Heat the sesame oil in a heavy, very large skillet over medium heat. Add the sausage slices and cook until browned and seared on both sides, turning once, about 6 minutes.
Split the baguettes in half lengthwise and remove excess bread so that the baguettes are about ½-inch thick. Spread the cut sides of the bread with the spicy mayo. Arrange the cucumber and jalapeño slices over the bottom halves of the bread. Top with the sausage slices, dividing them evenly. Spoon the pickled carrots over the sausage, dividing them evenly. Top with cilantro sprigs, dividing evenly. Close the sandwiches and compress them gently. (Sandwiches can be made ahead. Wrap them in foil or waxed paper and keep at cool room temperature up to 4 hours or refrigerate overnight.)
Excerpted with Permission from <a href="https://www.amazon.com/gp/product/0847847470/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0847847470&linkCode=as2&tag=craftfocom-20&linkId=dbe1d47ede12a2437c868ce77de1cb71">The Portable Feast: Creative Meals for Work and Play</a>.