Peel and chop onions. Heat the oil in a large 12" frying pan. Add onion and cook very gently, stirring with a wooden spoon, until soft- not brown, just golden. Press into this the garlic, using a garlic press. Blend in one can tomato paste, pimientos, chopping them and including their juice. Then add the peeled Italian tomatoes with basil, chopping the tomatoes likewise. Add pepper, basil, marjoram, a generous dash of tabasco and salt to taste. Simmer gently for 1/2 hour, stirring occasionally to prevent sticking. Transfer to the top of an extra large double boiler and stir in the strained lemon juice. Keep hot over boiling water. When ready to serve, drain the prepared cooked shrimp, add to the sauce and allow to heat through (about 10 minutes). In the meantime, cut the feta cheese into 1" cubes. Drop gently into the sauce, turn off heat, cover and allow to stand 5 minutes. Do not stir. Place the whole potful into a large, hot soup tureen, sprinkle with chopped parsley and serve at once at the table in large soup plates. Crisp, warm French bread should accompany this. Also chilled white wine.