To make Ginger-Garlic paste - place garlic, ginger, and canola oil in mini food processor and process to semi-smooth paste. Mix Ginger-Garlic Paste with coriander, turmeric, and 1/2 cup water in small bowl. This is a simple wet masala (spice mix). Set aside.
In large pot, warm oil over medium-high heat until shimmering but not smoking. Add serrano pepper, wait 30 seconds, then add cumin seeds and wait until they're done spluttering. Add wet masala (careful, it will also splutter). Cook until paste thickens, deepens in color slightly, and oil oozes out of the perimeter of the masala, about 2 minutes. Add cauliflower and potatoes, stirring to coat vegetables with masala. Season with salt and add 1/2 cup water. Cover and cook over medium heat 10 to 15 minutes. Remove lid, stir, and cook until the cauliflower and potatoes are cooked through, about 5 minutes. Garnish with cilantro and serve. A dollop of yogurt is good here too.