Cook the pasta according to the directions on the package.
Once the pasta is done cooking, rinse with cold water and place in a large mixing bowl. Combine pasta with remaining ingredients, reserving 1/3 cup sour cream. Make sure to break up the tuna into small pieces with a fork before adding it to the other ingredients.
This pasta salad is best if let sit for at least 4 hours (up to overnight) before serving. Stir in the remaining 1/3 cup sour cream just before serving.