Line a broiling pan with foil. Lightly oil the foil with a little olive oil.
In a large bowl, combine the lemon juice, olive oil, green onions, parsley, mustard, and mix well. Toss the chicken breasts in the mixture to cover.
Place the chicken breasts on the broiling pan.
Broil on the second highest rack of the oven for 10 minutes. Turn oven to bake at 325 degrees and bake for 20 minutes or until an instant read thermometer stuck into the thickest part reaches 135 degrees.
Remove pan from heat and let chicken sit for 5-10 minutes before serving.