In a large bowl, add the cooked and cooled rice, beans, corn, red pepper, red onion and cilantro. Stir with a rubber spatula or wooden spoon until evenly mixed together
Dressing
In a smaller bowl or measuring cup, add the lime juice, olive oil, vinegar, mustard, Tajin, cumin and salt. Use a fork or small whisk to stir it together to form a vinaigrette dressing.
Pour the dressing over the salad in the large bowl. Stir it well until combined.
Cover the bowl with a lid or plastic wrap. Refrigerate for at least one hour to allow the flavors to harmonize together before serving.