Bring a large pot of salted water to a boil and cook spaghetti until al dente. Reserve ½ cup pasta water, then drain and set aside.
Pat chicken pieces dry and season with salt, pepper, garlic powder, and paprika if using.
Heat olive oil in a large skillet over medium-high heat. Add chicken in a single layer and cook until golden and crispy, about 5-7 minutes. Remove from skillet and set aside.
Add more oil to skillet if needed, then sauté minced garlic until fragrant, about 30 seconds.
Stir in lemon zest and juice, then pour in chicken broth or reserved pasta water. Simmer 1-2 minutes to combine flavors.
Reduce heat to low and stir in butter if using until melted. Adjust seasoning with lemon juice, salt, or pepper.
Return spaghetti and crispy chicken to skillet. Toss to coat evenly with lemon-garlic sauce. Add extra pasta water if needed to loosen sauce.
Serve garnished with chopped parsley or basil and sprinkled with grated Parmesan if desired. Serve warm.