Cut a thin slice off the top of each tomato. Scoop out and discard pulp. Invert tomatoes onto paper towels to drain.
In a small mixing bowl, beat the cream cheese, feta cheese, sour cream, onion, lemon juice and oregano until blended. Pipe or spoon mixture into tomatoes. If desired, sprinkle with black pepper. Chill until serving.
Test Kitchen tips
To save time, you can prep the tomatoes and filling the night before your party, then fill the tomatoes before guests arrive.
If you don't have oregano on hand, substitute dried basil.