Heat the coconut oil in a large skillet over medium-high heat. Add the diced onion and cook for about 5 minutes until softened.
Reduce the heat to medium and stir in a pinch of baking soda. Continue cooking for about 10 minutes, stirring occasionally, until the onions become deeply caramelized.
Add the garlic and ginger and cook for 30 seconds.
Stir in the cumin seeds, mustard seeds, and crushed red pepper flakes. Cook for 2 minutes until fragrant.
Add the tomato paste and cook for another 3 minutes, stirring frequently.
Stir in the diced tomatoes, coriander, garam masala, turmeric, and salt. Scrape up any browned bits from the bottom of the pan.
Add the chickpeas and stir well.
In a small bowl, whisk the cornstarch into the coconut milk until smooth. Pour it into the pan and stir thoroughly.
Simmer uncovered for about 30 minutes until the sauce thickens beautifully. This Chickpea Curry develops even more flavor as it cooks.
Taste and adjust seasoning if needed. Finish with fresh lime juice and chopped cilantro.
Serve hot over basmati rice with naan and optional raita or tzatziki.