Heat the oil in a skillet over medium-high heat until it begins to get hot. Add the garlic, garam masala, cumin seeds, and turmeric and cook for 20 seconds. Add the tomatoes and cook for 2 minutes. Add the lentils and water and bring to a boil. Turn the heat to low and cook until the lentils are tender, about 30 minutes. Serve in a bowl and garnish with fresh cilantro sprigs.
To make garam masala:
Preheat the oven to 325 degrees F.
Combine the coriander seeds, cumin seeds, curry leaves, black peppercorns, mustard seeds, cloves, cardamom pods, cinnamon sticks, bay leaves, and chiles on a baking sheet and toast in the oven for 15 minutes.
Transfer the mixture to an electric spice grinder, or use a mortar and pestle and grind by hand. Grind to a fine powder. Store the garam masala in an airtight container for up to 3 months.
Can be found at specialty Asian and Indian markets.