Cook couscous according to package directions. Drain; add to a large bowl.
While the couscous is cooking, prepare the pesto. To the bowl of a food processor, add avocado, basil and walnuts. Pulse until the basil is finely chopped and the walnuts resemble coarse sand. While pulsing, slowly drizzle in the olive oil. Add nutrition yeast, lemon juice, garlic, salt and pepper; process until smooth with a little texture.
To the couscous, add pesto, white beans, tomatoes, cucumber and bell pepper. Mix until ingredients are well combined.
Serve immediately. Store in the refrigerator for up to 5 days.
Feel free to sub any whole grain for the couscous.