Preheat the oven to 375°F. Place the beets and 1⁄4 cup water in a small roasting pan, cover with foil, and roast for 40 to 50 minutes, or until the beets are just tender to the touch. Cool and peel the beets with a paring knife, and then cut each beet into quarters and set aside.
Meanwhile, combine the lentils and 3 cups of water in a small saucepan over medium heat. When the water boils, reduce the heat to a low simmer, add the salt and olive oil and cook, uncovered, stirring every 5 minutes, for 15 minutes, or until the lentils are still firm and intact, but starting to be creamy inside.
Drain any excess water, stir in the vinegar and garam masala, remove the pot from the heat, and transfer the lentils to a bowl to cool. If desired, add more salt, oil, vinegar, or garam masala to taste, then transfer lentils to a serving dish, garnish with the beets and greens, and serve warm or cold.