Preheat oven to 350°.
To prepare pita chips, split pitas; cut each half into 8 wedges. Arrange wedges in a single layer on a baking sheet. Bake at 350° for 20 minutes or until crisp. Cool completely on baking sheet.
To prepare cucumber cream, place spinach and sour cream in a food processor; process until smooth. Place spinach mixture in a small bowl; stir in cucumber and dash of salt. Cover and chill at least 1 hour.
To prepare dal, heat oil in a large saucepan over medium-high heat. Add cumin seeds and mustard seeds; cook 2 minutes or until toasted, stirring frequently. Stir in onion, garlic, red pepper, turmeric, and ginger; cook 1 minute, stirring constantly. Stir in broth, lentils, and 1 cup water; bring to a boil. Cover, reduce heat, and simmer 30 minutes or until lentils are very tender, stirring occasionally. Uncover and simmer 20 minutes or until thick and creamy, stirring occasionally with a whisk. Remove from heat. Stir in tomato, 1/4 teaspoon salt, and juice. Spoon about 3/4 cup dal into each of 4 bowls; top each serving with 3 tablespoons cucumber cream and 8 pita chips.