Slice each chicken breast horizontally to make 4 cutlets and cover with plastic wrap; pound gently to even thickness.
If marinating, place cutlets in buttermilk in a bag or container and refrigerate 30 minutes to 8 hours; when done, drain and pat dry, then lightly season both sides with salt.
To grill: preheat grill or grill pan to about 400°F (medium-high). Grease grates with a paper towel dipped in oil. Sprinkle both sides of chicken with lemon pepper and grill 4–6 minutes per side, until internal temperature reaches 165°F; tent and rest 5–10 minutes, then slice.
To cook in a skillet: whisk flour and lemon pepper in a shallow bowl. Heat butter and oil in a large pan over medium-high heat. Dredge cutlets in the flour mixture and cook 5–6 minutes per side until cooked through; tent and rest 5–10 minutes, then slice or chop.
Make the salsa: in a bowl combine drained cannellini beans, drained corn (or corn cut from the cob), chopped avocado, julienned sun-dried tomatoes and 2 teaspoons oil from the jar, chopped basil, 3 tablespoons lemon juice, and salt and pepper to taste; toss to combine.
Cook the couscous: bring chicken stock and 2 teaspoons butter to a boil in a small pot, remove from heat, stir in couscous, cover, and let sit 2–3 minutes until absorbed; fluff with a fork.
Stir 1/3 cup pesto, 2 tablespoons lemon juice, and about 1 teaspoon each salt and pepper into the couscous; taste and adjust seasoning.
Assemble bowls: divide the pesto couscous among 4 bowls, top with sliced chicken, and spoon generous amounts of the bean-corn-avocado salsa to the side. Drizzle remaining pesto over the bowls and serve with lemon wedges and fresh basil if desired.