In a large 6-quart or larger pasta pot, boil 4 quarts of water. Add 2 tablespoons of salt, then cook the pasta to al dente, or according to package directions. Drain the pasta into a colander in the sink, and rinse with cold tap water until the pasta has fully cooled. Let the pasta drain for a few minutes, shaking gently once or twice to remove any excess water that may have settled inside of the noodles.
In a 1-pint canning jar or lidded tupperware container, combine the lemon juice, olive oil, shallots, oregano, sugar, salt, and pepper. Shake vigorously to combine. Taste and season with salt or pepper as needed.
In a large mixing bowl, combine the pasta, vinaigrette, tuna and roasted peppers, tossing gently so as not to break up the pieces of tuna too much. Serve immediately or cover and refrigerate for up to a day.