How can I quickly save an unflavorful curry?

Indian curry traditionally has - in addition to the ginger, turmeric, cumin and chili (I assume you mean chili powder) that you used - a generous amount of garam masala, coriander powder, and garlic.

Sometimes you'll see "curry powder" used in recipes instead of garam masala; they are similar but not exactly the same.

Either one of these would be fine, and arguably the most important missing ingredient here. I'm not even sure you could legitimately call it a curry without one of the above.

Depending on your spice tolerance, you might need to add more chili powder as well.

Note that most spices in a curry will need to be heated before they'll really release their aromas (and therefore flavour), so you can't just add them cold, and I definitely don't think you'd want the taste of raw garlic/ginger in your curry, even if it is presently tasteless. Give it a good simmer after adding some garlic (powder is fine) and garam masala or curry powder and you might be able to salvage it.

Or you could try heating the new spices dry, for a very short time, to give them a bit of a head start aroma-wise; just be very careful not to burn them.

if it was me, I'd blend garlic and ginger (and fresh chillies if you want) to a paste into a small blender/coffee grinder (not one you actually use for coffee though), I'd warm some cumin and coriander seeds in a dry pan, then grind them down in a pestle and mortar.

Then I'd heat a table spoon of oil, add the spices back to it, fry for a few seconds, then add the garlic/ginger/chilli paste, cook that for a few mins on a highish heat and add to the curry. Then I'd season with lemon and salt/pepper.

you could also chop a handful of fresh coriander leaf and/or fresh mint and stir that through, which will give you a nice freshness and should compliment the lamb nicely.

If you have it, some tamarind loosened with a bit of hot water is a nice alternative to lemon, with a more savoury sourness, and can quickly add a bit of punch to a curry.

First suggestion is to check your seasonings. Adding various amounts of sweetener, salt, or acid (vinegar, lemon/lime juice, etc.) is the easiest way to bring out the flavors already there. Remember that the key when seasoning is to bring out the flavors already there - your dish shouldn't taste like salt, sugar, or acid. You can certainly try and add more spices, but that won't make a difference if your seasoning is off.

Second suggestion would be to remove some of the aubergine. By itself it doesn't have much flavor, so removing some of it to bring the rest of the ingredients in balance might help.

In Indian curries, you almost always fry onions, and add the spices to the frying onions (and continue frying for not too long.) It sounds like you're making "bangan bharta" like this recipe. Notice this step:

Heat oil in a pan, add garlic ,green chilli and chopped onions and fry over medium flame until light golden brown. Add red chilli powder, garam masala powder and turmeric powder.

That's what you should do, and add the onions to the final product. If you already have onions in your dish, just do this with less onion.

Also, don't forget the salt. Salt can really affect how much you can taste the other spices.

If you have one medium bowl or dish that you need to rescue, try the below steps:

1. First cut an onion into small pieces.
2. Cut a medium size of the tomato (To make it tangier).
3. Now take two tablespoons of oil, heat in a pan and put a half teaspoon of cumin.
4. Put, the cut onion in the pan. Just add salt for taste and cover it with a lid. Keep the lid closed till the oil float on all the sides. All this should be done in low flame.
5. Now after the oil floats on all the side add cut tomato and stir it with a ladle.
6. close the lid and cook for 3 mins. Now add your bowl of curry to the pan and mix it well and keep the lid closed till the oil floats on all the sides in slow flame.
7. Now the dish is cooked. Add some chopped coriander leafs.

The dish is ready to serve !!!

I recently made an eggplant curry using yellow Madras curry, onion, potato, sweet potato, fresh tomatoes, ginger paste, and coconut cream.

I sweated the onion first in some butter, added the dry spices and heated them before adding the harder vegetables (potato & sweet potato) and then added the softer tomatoes and eggplant with the coconut cream and let it all simmer.

My curry was great but still felt it was missing something; the next day I added heated it in a pan with a little lemon juice & a handful of fresh cilantro at the end. The acid and hit from the freshly wilted herbs added dimension and helped the other flavours pop. Lemon and cilantro are versatile since they can play nicely with either an Asian or an Indian spice palette.

Note: the photo I have attached is from the first day I made it without the herbs added.