In a large, high-sided skillet over medium heat, melt butter. Add onion and ½ tsp. salt and cook, stirring occasionally, until softened, about 7 minutes. Add tomato paste and cook, stirring constantly, until darkened, 4 to 5 minutes. Add chile and ginger and cook, stirring, until fragrant and tomato paste is starting to stick to bottom of pan, about 1 minute more.
Add chickpeas and baking soda and stir to combine, then add garam masala, cumin, and chili powder and cook, stirring frequently, until fragrant and incorporated, about 30 seconds.
Stir in cream, 1 cup water, fenugreek (if using), and ½ tsp. salt. Bring to a simmer over medium-high heat, then reduce heat to low and continue to simmer, stirring occasionally, until sauce is reduced, 10 to 15 minutes; season with more salt, if needed. Top with cilantro.
Divide rice among bowls or plates. Spoon chickpea mixture over rice.
