Roast the fenugreek and onion seeds first by heating and tossing in a sauté pan for several minutes. Grind them together using a mortar and pestle or spice grinder.
In a food processor, blend fenugreek and onion seeds with the salt, garam masala, turmeric, curry powder, coriander powder, cumin, chili powder, paprika, garlic, vegetable oil, ginger, jalapeños, cilantro and lemon juice until all the ingredients become a smooth paste.
Spoon the mixture into a large mixing bowl and stir in the yogurt.
Marinate meat or fish for eight hours (or bathe first in white distilled vinegar for shorter marination time). Tofu, vegetables or paneer can be tossed into the marinade just before grilling. Use the marinade to baste over the grill.