Start by boiling water in a pot and when the water has reached a boiling point pour the rice in the pot and leave it cook, stirring occasionally.
Meanwhile the rice cooks, pour half of the olive oil in a pan and fry the chicken breasts until they get golden on both sides. When they are done remove them, cut them in small slices and place them in a bowl.
At this point if the rice is done remove it and place it on a colander, if not let it continue cooking, then pour the remaining oil in a pan and fry the mushrooms for 5-6 minutes and when they are ready add them together with the oil on the bowl with the cooked chicken breast.
Wash and cut the cherry tomatoes in 2 pieces and pour the rice in a big bowl. Mix together the rice, the chicken breast, the cherry tomatoes, the leek and the mushrooms and serve the food when it is till warm.