Flatten turkey rolls lightly with a meat tenderizer. Peel onion and cut into small cubes. Rinse lettuce and pat dry. Set some small leaves aside and cut the rest into finger-thick strips. Cut feta cheese into two thick strips. Braise onion in a little water for 5 minutes.
Add lettuce to onion pan, season with salt and pepper and simmer, covered, for 2-3 minutes. Uncover and simmer on high heat briefly. Spread turkey cutlets with mustard. Then spread with lettuce filling and feta strips. Roll up and secure with wooden skewers.
Cook rice according to package instructions. Heat oil in a pan and cook rolls on all sides on medium heat for a few minutes. Add chopped rosemary, diced tomatoes and 3 tablespoons of water to the pan and simmer for 8 minutes more. Arrange turkey rolls with tomato sauce and rice on plates and serve garnished with lettuce leaves.