Rinse the lentils under running water and add them to a large pot of rapidly boiling salted water. Return to a simmer and cook until they are tender, 20 to 30 minutes. Drain the lentils, rinse under running water to stop the cooking and let them cool.
Stir the lentils, chives and garlic together in a large bowl with 2 tablespoons olive oil. Season with with 1/2 teaspoon salt and one-eighth teaspoon pepper.
Stir in the cucumber, cherry tomatoes, onion and lemon juice. Gently fold in baby spinach. Add just enough olive oil to moisten the baby spinach (you may not need to add any). Stir in the pine nuts and season with more salt and pepper to taste. Serve at room temperature.