1. Lightly grease an oven-proof dish, approximately 9 inches diameter and 3-4 inches deep (or half the recipe and use a 9 inch pie-dish).
2. Remove skin and bones from salmon and lightly stir-fry (in 1 tsp of oil) for 3 minutes, breaking tuna into small chunks and ensuring no bones remain. Remove from pan and set aside.
3. Lightly stir-fry spinach leaves (adding an additional tsp of oil if required) , for 2 minutes. Remove from pan and set aside.
4. Lightly stir-fry mushrooms (adding an additional tsp of oil if required) for 2 minutes. Remove from pan and set aside.
5. Beat together egg whites and milk.
6. Mix salmon, mushrooms, spinach, can of tomatoes, 2/3 cups crushed potato chips together with egg white mixture.
7. Stir well.
8. Tip mixture into baking dish.
9. Cover with sliced tomatoes ad 1/3 cup of crushed potato chips (Optionally you may add 3/4 cup grated cheese to the topping).
10. Bake covered at 350 F for 30 minutes.
11. Remove cover and bake an additional 45 minutes, or until set.
12. Test by putting a knife in center to see if it comes out clean or feels firm.
13. Serve hot or warm. Buen provecho!