How to Make It
In a medium saucepan, toast the seeds over moderate heat for 2 minutes. Coarsely crush.
In the same saucepan, heat the oil. Add the onion, season with salt and cook over moderate heat, stirring occasionally, until softened, 5 minutes. Add the vinegar, sugar and 1 tablespoon of the ginger and cook, stirring occasionally, until the vinegar is slightly reduced, 2 minutes. Add the mangoes, crushed seeds and crushed red pepper and cook over moderately high heat, stirring, until the mixture resembles jam, 5 minutes. Scrape the chutney into a small bowl and let cool. Season with salt.
Heat a griddle over moderately low heat. In a large bowl, toss both cheeses with the jalapeño, cilantro and remaining 2 teaspoons of ginger. Season with salt and black pepper.
Brush 1 side of each bread slice with butter. Arrange 4 slices buttered side down on the griddle. Top each with one-fourth of the cheese mixture and 3 tablespoons of the chutney. Close the sandwiches and cook until golden, 3 minutes per side. Let rest for 2 minutes, then cut in half and serve.