Soak the sliced red onions in cold water for 5-10 minutes. Drain water and pat dry red onions using paper towels.
In a large bowl, toss together the spring mix salad, sliced red onions, sliced red radishes, and avocado wedges.
Blend fresh cilantro with olive oil in a food processor and transfer to a small bowl. Add the low-sodium soy sauce, lime juice, and honey and mix well until the honey is well dissolved in the sauce.
Add the smoked salmon into the salad mix and pour the cilantro lime vinaigrette over the salad. Toss to coat and top with chopped toasted walnuts.