I own the same book and was similarly surprised when I read that instruction, but in the section on ingredients, the author does mention a particular variety of onions called pink onions. The mention is on pg. 32, and there is a picture of a pink onion on the upper left of pg. 34.
Here's an excerpt from pg. 32:
"The longer the onions are fried, the browner they will get and the deeper the color of the curry will be... When the onions are fried until only light pink in color, they will impart a sweetish taste to the curry. Certain varieties of onion, like Spanish onions, are too sweet to be appropriate for curry-making. The most appropriate from the taste point of view are the French and the small pink English."
From 50 great curries of india
I've never seen pink onions in any of the local markets (in northwestern US), I used white onions and sauteed them just to the point of browning. The recipe turned out fine, but it's a lot of onion. (The recipe calls for 2 large onions, finely chopped. It's a recipe that produces 2 servings.) Personally, I'd go a little lighter on the amount of onion or use yellow onions (despite the author's recommendation against Spanish onions), but that is just personal preference from a Western palate.
Note: it looks like the current printing of the book is different from the one I own, so the page numbers I cite may be off, but if you search inside the book (on Amazon) for "pink onion" you can see the page I've cited and the picture of what the author calls a pink onion.
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.
Best Answer
For reference, a sheekh kebab is spiced minced meat pressed onto a skewer and barbecued. There are no binding agents like egg or breadcrumbs in a traditional recipe, so you want to avoid any extra moisture in your ingredients or it may not hold together.
An authentic recipe will call for green chilies, not green peppers. The chilies need to be the your birds eye style, narrow tapered chilies with thin walls, not thick walled chilies like jalapenos because they contain too much moisture. Bell peppers are not a substitute for the same reason.
There are many green chili varieties which would work in the recipe, and they vary from mild to tonsil-searing. Which to use depends on how hot you want the result to be and what's available in your local area. If you don't want that spicy and all you can find are hot ones then de-seed them and just add less - it's all getting pureed anyway.
Tips for making good meatballs and mince-based kebabs: