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.
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.