An hour or two ahead if possible place the chicken breasts in a shallow dish. Pour over the lemon juice, olive oil and seasoning.
Prepare the salad – put the sliced fennel in a large bowl, in another small bowl mix the olive oil, lemon juice and mustard together, taste for seasoning. Mix the fennel and dressing together – set aside.
Seal the chicken breasts on a hot pan until well browned. Then finish cooking in the oven for 10-15 minutes.