In a small bowl, combine lemon juice, pepper and salt. Pour over mackerel and set aside for 10 minutes.
While mackerel are marinating, prepare the sauce. Mix together yogurt, sandwich spread and mustard.
Stir in chopped parsley and salt. Set aside and put in a refrigerator.
Heat oil in a pan and saute garlic until it becomes slightly brown.
Arrange mackerel halves in the pan, being careful not to break them.
Fry the fish for 1 minute on one side, gently flipping over and fry the other side for another minute.
Transfer to a serving plate. Pour excess olive oil and garlic bits on top pf sardines. Serve with the sauce.
If you want to use it for pasta, before marinating the canned mackerel, break it into large flakes, increase amount of salt to 1/2 teaspoon and minced garlic to 2 tablespoons. After frying, toss with cooked spaghetti pasta, and sprinkle with Parmesan cheese.