Prepare the tomato and onion salsa: Combine chopped tomatoes, red onion, crushed garlic, salt, pepper, red wine vinegar, and olive oil in a bowl.

Stir salsa well and let it sit for at least 30 minutes for flavors to meld.

Boil the potatoes whole in salted water until tender.

Let potatoes cool slightly, then slice thinly.

In a large bowl, whisk eggs, ricotta cheese, and Parmesan cheese until smooth.

Stir in chopped parsley and basil.

Season the egg mixture with salt and pepper to taste.

Preheat the broiler.

Oil a large, nonstick frying pan.

Pour half of the egg mixture into the pan.

Arrange the potato slices evenly on top of the egg mixture.

Pour the remaining egg mixture over the potatoes.

Cook over low to medium heat for 10-15 minutes, or until the frittata is set.

Place the frittata under the broiler for 2-3 minutes to lightly brown the top.

Carefully slide the frittata onto a cutting board.

Let the frittata cool slightly.

Arrange watercress on a serving platter.

Cut the frittata into wedges.

Place the frittata wedges over the watercress.

Spoon the tomato and onion salsa over the frittata.

Serve warm or at room temperature.