Pat the chicken dry with paper towels and cut it into roughly 1-inch pieces. Place it in a bowl and toss with smoked paprika, Italian seasoning, black pepper, onion powder, garlic powder and salt.
Heat a large skillet over medium-high heat and add the olive oil. Once hot, add the chicken in a single layer, working in batches if necessary to prevent overcrowding.
Cook the chicken for 2–3 minutes without moving it so it can brown properly. Turn the pieces and continue cooking until browned on several sides and nearly cooked through. Transfer the chicken to a plate.
Reduce the heat slightly and add the trimmed green beans to the same skillet. Cook for approximately 4–5 minutes, stirring occasionally. If needed, add 1–2 tablespoons of water and cover briefly to help the beans become tender-crisp.
Add the sliced onion and cook for another 2–3 minutes until softened.
Add the butter and minced garlic. Stir continuously for 30–60 seconds, just until the garlic becomes fragrant. Do not let it burn.
Reduce the heat to low. Stir in the Greek yogurt, Parmesan and lemon juice. Mix gently until the ingredients form a smooth, creamy coating. If the sauce is too thick, add a tablespoon or two of water or low-sodium chicken broth.
Return the browned chicken to the skillet and stir gently to coat everything in the sauce. Cook for another 2–4 minutes, or until the chicken reaches a safe internal temperature and the sauce is hot.
Taste and adjust the salt, black pepper and lemon juice as desired. Add red pepper flakes if you want some heat.
Remove the skillet from the heat and let it rest for a couple of minutes before serving. Divide into five portions and serve warm.