Heat 1 tbsp. olive oil on high in a large skillet with a lid. Add Brussels sprouts, cut side down. Turn the heat down to medium and let the sprouts brown, 5 minutes. Stir and cover; let steam another 5 minutes. Take the sprouts off the heat, remove from pan and let cool.
Heat 1 tbsp. olive oil in the same skillet, toss in the whole cumin seeds and the mustard seeds till fragrant, 20 seconds. Stir in the remaining spices and heat for another five seconds.
Add the garlic, ginger, and onion and cook on medium high heat, stirring occasionally till translucent, 6 minutes.
Add the tomatoes and cook on medium high heat till the onions start to caramelize and the tomatoes are reduced, 7 minutes.
Add the remaining olive oil and stir.
Add the browned Brussels sprouts and season with salt. Let cook until heated through, about 3 minutes.
Remove from heat, top with the chopped cilantro and serve warm.