In a bowl, mix together Dijon mustard, juice, and zest from two lemons, chopped rosemary, pepper flakes, olive oil, and salt and pepper.
Whisk the mixture together.
Place the chicken in the baking dish (9x13").
Brush the mixture over the chicken; leaving a couple of tablespoons for re-painting during the roasting process.
Cover the chicken with the plastic wrap and refrigerate for at least 2 hours up to overnight.
Preheat the oven to 400 degrees F.
Slice 1 Meyer lemons and place it on top of the chicken, squeeze the juice from the remaining lemon all over the chicken and add few sprigs of rosemary on top.
Roast chicken for 40 to 45 minutes until the internal temperature reaches 165 degrees F.