1- In a bowl, mix the olive oil and harissa well with a fork.
2- Using a sharp knife, cut the chicken breasts across, taking care not to separate the halves, and flatten the two pieces into a butterfly shape.
3- Season the inside of each chicken breast with salt and pepper. Place a few slices of lemon and a sprig of thym on one side. Fold the other side to close the chicken breast.
4- Place the chicken breasts in a shallow dish and drizzle with the harissa-olive oil mixture. Let marinate for 30 minutes, turning the chicken pieces twice.
5- Heat a saucepan. Add the stuffed chicken breasts with lemon. Cook for 3 minutes. Add 1 cup of water and cover.
6- Cook for 15 minutes over medium heat.
7- Cut the tomatoes into thin slices.
8- To serve, place some couscous on each plate. Place the tomato slices next to the couscous.
9- Transfer a chicken breast to the tomatoes on each plate. Serve immediately.