Place a large pot of salted water over high heat and bring to a boil. Meanwhile, chop the chicken, onion, and herbs. Place a large skillet over medium heat and add the butter and oil.
Drop the pasta in the boiling water and cook as instructed on the package (about 8 minutes) then drain. Once the butter is melted, salt and pepper the chicken liberally and toss with 2 tablespoons flour. Place the chicken pieces in the hot butter and saute for 2-3 minutes per side until golden brown. Remove the chicken with a slotted spoons and place on paper towels to dry.
Add the rosemary, garlic and onions to the butter and saute for 1 minute. Then whisk in the remaining 2 tablespoons flour to thicken the sauce. Cook for another minute, then whisk in the lemon juice and chicken stock.
Once the sauce is simmering again, toss in the pasta, capers and parsley. Mix in the chicken and serve warm.