Preheat oven to 425º F. Arrange the tomatoes in a single layer on a baking sheet. Drizzle with 2 tablespoons of the olive oil; season with the salt and 1/4 teaspoon pepper. Scatter the thyme on top. Place in oven and bake until the tomatoes are soft, 15 to 20 minutes. Set aside to cool.Divide the cooled pasta among 6 large bowls. Spoon some the ricotta over each serving. Top with some of the tomatoes and thyme sprigs. Drizzle with olive oil and sprinkle with lemon zest and pepper to taste just before serving.