Season chicken breasts with salt, pepper, and olive oil.
Grill or pan-sear chicken over medium-high heat for 6-7 minutes per side until internal temperature reaches 165°F (74°C).
Rest chicken for 5 minutes, then dice into small cubes.
In a blender, combine Greek yogurt, basil, parsley, garlic, shallot, lemon juice, rice vinegar, walnuts, and nutritional yeast. Blend until smooth.
In a large mixing bowl, combine chopped cabbage, cucumbers, green onions, and spinach.
Add the diced chicken to the vegetable mixture.
Pour the dressing over the salad and toss thoroughly until all ingredients are evenly coated.
Serve immediately or store in an airtight container for meal prep.