Cook pasta according to package directions. Drain well.
Combine parsley, Parmesan cheese, feta cheese, oil, water, basil, and garlic powder in a mixing bowl. Stir in cooked pasta.
Remove stems from tomatoes. Cut plum tomatoes in half lengthwise. Spoon out seeds and center membrane. If using cherry tomatoes, slice a thin layer off the round end of each one to make them stand upright. Using a small spoon, scoop out and discard the pulp, leaving a 1/4-inch-thick shell. Invert tomatoes and drain on paper towels. Place tomatoes, right side up, on serving plate. Spoon or pipe pasta mixture into tomatoes. Cover; refrigerate 8 to 24 hours.
To serve, let tomatoes stand at room temperature 30 minutes.