Bring a large pot of salted water to a boil. Cook the pasta until al dente according to package directions. Drain, rinse and set aside to cool.
While the pasta is cooking, toss the thinly sliced onion with 1 tablespoon red wine vinegar.
Chop the vegetables and make the dressing: whisk together the remaining 2 tablespoons red wine vinegar and olive oil along with the sugar, garlic clove and generous pinch salt and pepper (will depend on your pasta water that you salted, but I usually do ~1/2 teaspoon each).
Drain any excess liquid off the onions, then toss with the cooked pasta, vegetables, herbs and dressing. Toss well to combine, season to taste, and enjoy.