Combine the lemon juice, mustard, garlic and white pepper. Beat in 5 tablespoons of the olive oil. Put the chicken in a shallow container and pour the lemon mixture over it. Cover and refrigerate for at least 1 hour.
In a large frying pan, saute the almonds in 1/2 tablespoon of the olive oil until golden. Remove from pan and reserve. Wipe out the pan. Drain the chicken, reserving the lemon marinade. Add remaining 1 tablespoon olive oil to pan, then add chicken breasts and brown over high heat until brown on each side (6 to 10 minutes). Remove from pan and reserve.
Strain the lemon marinade into the pan. Bring to the boil and boil for 1 minute. Add chicken stock and cornflour/water mixture. Cook over high heat, stirring occasionally, until the mixture reduces by half (about 5 minutes). Add marmalade and stir over medium heat until melted. Stir in the butter a bit at a time over high heat, stirring constantly. Stir in parsley and red chilli flakes. Return chicken to pan and heat through. Add reserved almonds and garnish with lemon slices.