Bring a large pot of water to a boil. Cook the whole wheat penne according to package directions until al dente. Reserve 1 cup of the pasta cooking water, then drain.

While the pasta cooks, heat olive oil in a large skillet over medium heat. Add chicken pieces and season with black pepper. Cook for 5–7 minutes, stirring occasionally, until the chicken is cooked through and lightly golden. Add minced garlic and cook for 30 seconds until fragrant.

In a blender or food processor, combine cannellini beans, pistachios, Greek yogurt, garlic, lemon zest and juice, salt, black pepper, and half the reserved pasta water. Blend until very smooth and creamy. Add more pasta water as needed to reach a pourable, sauce-like consistency.

Add drained pasta to the skillet with the chicken. Pour in the creamy lemon–pistachio sauce and toss gently over low heat for 1–2 minutes until everything is evenly coated and warmed through.

Taste and adjust seasoning with extra pepper or lemon juice if desired. Serve warm.