You could, of course, top this macaroni and cheese with store-bought salsa, but it takes only minutes to make your own. Slideshow: More Macaroni and Cheese Recipes
Preheat the oven to 350°. Butter 4 small soufflé dishes or a shallow 1 1/2-quart gratin dish.
To make the macaroni and cheese, heat the olive oil in a medium skillet over moderate heat. Add the bacon and cook until crisp and browned, 5 to 8 minutes. Using a slotted spoon, transfer the bacon to a paper towel–lined plate. Set aside.
Add the jalapeño to the skillet and cook until softened, 2 to 3 minutes. Add the flour and cook, stirring until smooth, about 1 minute. Add the milk and cook over moderately low heat, stirring occasionally, until thickened, about 10 minutes. Add all but 1/2 cup of the cheese and stir until melted and smooth. Season with salt and pepper, and keep the sauce warm over very low heat.
Meanwhile, in a medium saucepan of boiling well-salted water, cook the pasta until al dente. Drain well and add to the cheese sauce, stirring well to coat. Divide the macaroni and cheese between the soufflé dishes or pour into the gratin dish, then top with the remaining cheese. Sprinkle the reserved bacon over the macaroni and cheese.
Bake until golden and bubbling, 15 to 20 minutes.
While the macaroni and cheese bakes, make the salsa: Stir together the tomato, jalapeño, onion and cilantro in a small bowl and season with salt.
Top each portion of macaroni and cheese with some of the salsa, and serve.