How to Make It
Rinse the quinoa in 3 changes of water in a bowl, rubbing the grains and letting them settle each time before pouring off the water (if the quinoa does not settle, drain in a large fine-mesh sieve after each rinse).
Cook the quinoa in a medium saucepan of boiling well-salted water until tender, about 15 minutes. Drain well in a sieve.
While the quinoa cooks, stir together the onions, jalapeño, olive oil, lime juice and cumin in a large bowl. Season to taste with salt and pepper. Add the warm quinoa to the dressing, along with the black beans, corn and cilantro. Toss gently to combine. Serve warm or at room temperature.