Mix the tomato paste with 3 tablespoons of water and set aside.
In a large, heavy skillet with a cover, heat the oil until it is fragrant. Add the onion and saute over high heat, stirring frequently, until they start to brown a little, about 4 minutes. Lower the heat and continue cooking, stirring often, until the onion turns golden brown, about 10 minutes more.
Add the garlic, and garam masala, lower the heat to medium-high, and saute for another 2 minutes. Stir in the ground spices and saute another 2 minutes. Add the cubed lamb, stir well, and brown it in the spices for about 5 minutes.
Add the tomato paste and cardamom seeds and stir well. Lower heat, cover pan tightly, and simmer about 30 minutes, stirring occasionally and adding more water by tsp if sauce starts to stick to the pan.
Uncover the pan and stir in the lemon juice and salt, to taste. Simmer uncovered about 10 minutes longer, stirring frequently, until the meat is tender and the sauce is very thick.