These meatballs have an unexpected complex flavor. Baking them means you won't get quite the contrast of textures as you might from pan-frying, but it's so much easier (and less messy) that it's worth the trade-off. You can mix up the spices, but be sure to use something pungent. —MeghanVK
Heat the butter or oil in a saute pan on low heat. Cut the onion in half and slice it thinly (a mandoline will make short work of this) and add to the pan. Allow to caramelize for 20-30 minutes, stirring occasionally so they don't burn. Once the onions are a deep brown, reserve half and finely chop the rest.
Wipe out the saute pan and toast the cumin, coriander, and fenugreek seeds until fragrant, and then grind them in a grinder or mortar and pestle.
Preheat the oven to 350. In a mixing bowl, use your hands to combine the ground turkey with the lemon zest, bread crumbs, egg, chopped caramelized onions, and spice mixture. Season with salt and pepper. Shape the mixture into small meatballs, about an inch and a half in diameter. Place the meatballs on a lined baking sheet and bake for 20 minutes, rotating the sheet halfway through. They are done with they are cooked through and slightly browned around the edges.
To serve as a fancy hors d'ouevres, smear a plate with Greek yogurt, drizzle with olive oil and lemon juice, and place the meatballs, on toothpicks, in the yogurt. Drape with the caramelized onions. For a heartier meal, mix all of the above with spaghetti, thinning the yogurt with pasta cooking liquid as necessary.