Preheat the oven or toaster oven to 425°F (220°C).
Wash the brussels sprouts thoroughly, and then chop off the bottoms just enough to peel off individual leaves. Peel off several leaves from each sprout, or enough that the leaves no longer easily peel off.
Chop the remaining sprouts in half, then put them with all the leaves into a mixing bowl. If your brussels sprouts still have a fair amount of water clinging to them, line a baking tray with a piece of aluminum foil and add your sprouts, then out them in the preheating oven for 2-3 minutes. They'll be slightly wilted and greener, but dry enough to fry rather than steam.
Wash and mince your cloves of garlic, then measure all your spices (turmeric, cumin, coriander, nigella seeds, ginger, mustard & amchur), and add them to the mixing bowl along with the oil, salt, and coconut sugar.
Toss together all the ingredients (except the lemon juice) until evenly coated, then pour them onto the baking tray and put them in the oven. Do NOT clean the mixing bowl, yet.
Bake for 5 minutes on convection, then move them around and turn the tray to ensure even baking. Cook for 4 more minutes, then take them out again and remove any leaves that are crispy and somewhat browned, then return them to the oven for 3 more minutes.
Once you've removed the tray from the oven, immediately transfer the sprouts back into your mixing bowl and toss them all with lemon juice (if using). Try one bite and add extra salt as needed. Serve and enjoy!