Place the bacon in a large frying pan and cook over medium-high heat, turning occasionally until evenly browned, about 10 minutes. Drain the bacon on a paper towel lined plate. Let cool then crumble into small pieces.
Mix bacon and feta together in small bowl. Cut a 5-6cm slit lengthwise in the side of the chicken breast creating a pocket and fill with mixture. Secure shut with toothpicks.
Place chicken in slow cooker then add tomatoes and basil. Cook on High until chicken is no longer pink in the centre, about three hours.